# Late Antique Basilia - a fortified settlement on the cathedral hill in Basel (Switzerland). Changes in urban land use based on archaeological and geoarchaeological evidence

Christine Pümpin, Markus Asal, Philippe Rentzel

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Christine Pümpin, Markus Asal, Philippe Rentzel. Late Antique Basilia - a fortified settlement on the cathedral hill in Basel (Switzerland). Changes in urban land use based on archaeological and geoarchaeological evidence. Quentin Borderie; Ferréol Salomon. Urban Geoarchaeology, CNRS Éditions, pp.291-306, 2024, 9782271149299. hal-05321734

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Scientific editors:
Quentin Borderie and Ferréol Salomon

Urban Geoarchaeology

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The global spread of urbanisation is having a profound impact on environments, climates and social lives. This gives rise to questions about the sustainability of urban areas, the management of soils and sediments and the socio-environmental construction of spaces. Archaeological investigations show that societies produced a wide variety of different urban forms throughout millennia and across continents. By focusing on human-environment interactions through the study of soils and sediments, geoarchaeological research provides new insights into the different ways of making and living in a city in the long term.

With twenty four contributions written by researchers from all over the world, *Urban Geoarchaeology* expands our knowledge of human-environment interactions and ancient urban lifestyles. This volume brings together substantial and comprehensive elements to understand past urban systems, using new interdisciplinary approaches, case studies of broad interest, and innovative techniques to answer historical questions. It shows how geoarchaeologists are producing and discussing new data on the transformation of landscapes through urbanisation. Processes of urban stratification over time are also better understood. The construction of urban spaces can be analysed from the large scale of the urban systems to the microscale of the soil formation, revealing ancient activities and lifestyles. Finally, *Urban Geoarchaeology* helps to connect the past, the present and the future of our cities.

Quentin Borderie is a field geoarchaeologist, based in Avignon (France), working on the urban environment for twenty years, giving courses at La Sorbonne University. He contributes to the research on urban Dark Earths, floor formation processes, and stratification dynamics in urban areas. He is attached to the CNRS laboratory UMR 7041-ArScAn, in the "Archéologies Environnementales" team.

Ferréol Salomon is a researcher in geoarchaeology at the French National Centre for Scientific Research (CNRS) and based in the Laboratoire Image Ville Environnement at Strasbourg (UMR-7362). His research focuses on human-nature interactions between urban societies and deltaic environments over the last millennia. He studied different urban sites in south-west Asia and across the Mediterranean area.

Cover image:

From left to right: Sedimentary drilling in Ostia (Italy) within the Roman city; archaeological excavation in Beauvais (France) from the top of the 16th century cathedral showing Dark Earths and an 11th century church; star shaped vivianite crystal and a bone through optic microscope cross-polarised light; aerial view of Metz (France) and the Mosel River.

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9 782271 149299

69 € prix valable en France

ISBN : 978-2-271-14929-9

www.cnrseditions.fr
Urban Geoarchaeology

Scientific editors: Quentin BORDERIE and Ferréol SALOMON

CNRS ÉDITIONS

15 rue Malebranche - 75005 Paris
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Laboratoire

image, ville, environnement | LIVE

de l'Université de Strasbourg

de l'ÉNOLES et du

Université

de Strasbourg
<table>
  <tbody>
    <tr>
      <td>2.6. Ancient maps, geotechnical and (geo)archaeological data: GIS integration for the understanding of archaeological sites and for decision making in rescue archaeology</td>
      <td>241</td>
    </tr>
    <tr>
      <td>Hervé Tronchère-Cottet, Corentin Martinez, Catherine Pothier, Cyrille Ducourthial</td>
      <td></td>
    </tr>
    <tr>
      <td>Section 3 – Building urban spaces: Social spaces, Activities and lifestyles</td>
      <td>261</td>
    </tr>
    <tr>
      <td>Short introduction: Quentin Borderie, Ferréol Salomon</td>
      <td></td>
    </tr>
    <tr>
      <td>3.1. The geoarchaeology of urban ecclesiastical sites in coastal locations; Exeter, UK and Trondheim, Norway.</td>
      <td>267</td>
    </tr>
    <tr>
      <td>Richard Macphail, John Allan, Chris Carey, Ingeborg Sæhle</td>
      <td></td>
    </tr>
    <tr>
      <td>3.2. Activities written in the house floors in urban space of Medieval Brno, Czech Republic.</td>
      <td>279</td>
    </tr>
    <tr>
      <td>Lenka Lisá, Antonín Zůbek, Marek Peška</td>
      <td></td>
    </tr>
    <tr>
      <td>3.3. Late Antique Basilia – a fortified settlement on the cathedral hill in Basel (Switzerland). Changes in urban land use based on archaeological and geoarchaeological evidence</td>
      <td>291</td>
    </tr>
    <tr>
      <td>Christine Pümpin, Markus Asal, Philippe Rentzel</td>
      <td></td>
    </tr>
    <tr>
      <td>3.4. Geoarchaeology in peri-urban environment: a soil micromorphological case study of the “Land of Aynadamar” in Nasrid, Granada (Spain), the northern outskirts of the last Islamic town in Iberia (13th – 16th centuries).</td>
      <td>307</td>
    </tr>
    <tr>
      <td>Rowena Y. Banerjea, Guillermo García-Contreras, Marcos García-García, Luca Mattei, Aleks G. Pluskowski</td>
      <td></td>
    </tr>
    <tr>
      <td>3.5. Prelude to the urban – a study of the monumental earthen architecture of the pre- and early historic site of Arslantepe (Turkey).</td>
      <td>323</td>
    </tr>
    <tr>
      <td>Susanna Cereda</td>
      <td></td>
    </tr>
    <tr>
      <td>3.6. Urban garden soils – evidence of medieval and early modern horticulture in European towns</td>
      <td>341</td>
    </tr>
    <tr>
      <td>Jens Heimdahl, Mateusz Krupski</td>
      <td></td>
    </tr>
    <tr>
      <td>Section 4 – Connecting the past, the present and the future of cities</td>
      <td>359</td>
    </tr>
    <tr>
      <td>4.1. Climate changes, natural hazards and resilience of urban areas.</td>
      <td>361</td>
    </tr>
    <tr>
      <td>Short introduction: Ferréol Salomon, Quentin Borderie</td>
      <td></td>
    </tr>
    <tr>
      <td>4.1.1. The urban geoarchaeology of imperial China: A case study of the urban renewal and decline of two capital cities, Luoyang and Kaifeng.</td>
      <td>365</td>
    </tr>
    <tr>
      <td>Michael J. Storozum, Peng Lu, Panpan Chen, Hui Wang, Xiaolin Ren, Junna Zhang, Zhen Qin, Xiaotao Guo, Tao Liu, Sanying Wang, Qifeng Ge, Haiwang Liu</td>
      <td></td>
    </tr>
    <tr>
      <td>4.1.2. Fate of two cities built on sinking ground: slow and fast submergence at Thônis – Heracleion and Canopus, Nile River Delta, Egypt</td>
      <td>381</td>
    </tr>
    <tr>
      <td>Gilles Brocard, Jean-Philippe Goiran, Damian Robinson</td>
      <td></td>
    </tr>
    <tr>
      <td>4.1.3. Resilience research in geoarchaeological investigations of Mediterranean urban sites</td>
      <td>401</td>
    </tr>
    <tr>
      <td>Rachel Kulick</td>
      <td></td>
    </tr>
    <tr>
      <td>4.2. Urban geoarchaeology towards future cities.</td>
      <td>417</td>
    </tr>
    <tr>
      <td>Short introduction: Ferréol Salomon, Quentin Borderie</td>
      <td></td>
    </tr>
    <tr>
      <td>4.2.1. Urban geoarchaeology and local administration: methods and approaches. The case of the ancient port town of Fréjus (France).</td>
      <td>421</td>
    </tr>
    <tr>
      <td>Pierre Excoffon, Stéphane Bonnet, Grégory Gaucher</td>
      <td></td>
    </tr>
    <tr>
      <td>4.2.2. When urban geoarchaeology is explained to all types of audiences: the case of Lyon, France.</td>
      <td>431</td>
    </tr>
    <tr>
      <td>Stéphane Gaillot, Laurent Strippoli</td>
      <td></td>
    </tr>
    <tr>
      <td>Geoarchaeology: towards new interdisciplinary challenges and opportunities in the understanding of urban environments</td>
      <td>443</td>
    </tr>
    <tr>
      <td>Ferréol Salomon, Quentin Borderie</td>
      <td></td>
    </tr>
    <tr>
      <td>Urban Geoarchaeology and complexity</td>
      <td>447</td>
    </tr>
    <tr>
      <td>Denise Pumain</td>
      <td></td>
    </tr>
  </tbody>
</table>
Acknowledgements

We, the scientific editors, would like to thank all the contributors of this book for their work in preparing their excellent chapters and their quick and positive answers all along the preparation of this publication. We are also very grateful to all the anonymous reviewers that we contacted and who provided very helpful comments to improve all texts and figures of the contributions. A special thank you to the two anonymous reviewers contacted by the *Pôle d'appui à la publication* (Publication Support Service) of the University of Strasbourg that read the entire book, including main introductions and conclusions. They gave very good advice and suggestions to ameliorate the manuscript before the final submission to CNRS Editions. We also thank Prof. Denise Pumain for the conclusive remarks and Dr. Leah Holguin for the English proof-reading.

We would also like to thank CNRS Editions for publishing this book. Additionally, we thank the *Pôle d'appui à la publication* of the University of Strasbourg, Barbara Weisbeck and all members of the committee who evaluated and financially supported this publication.

This book would also not have been possible without the financial support of the *Département de Vaucluse*
(many thanks to Emilie Fencke, the Cheffe du Service Archéologie), the joint CNRS-Universities research units
of the *Laboratoire Image Ville Environnement* (https://live.unistra.fr/ – UMR-7362) and of *Archéologie et Sciences
de l'Antiquité - ArScAn* (http://www.arscan.fr/ – UMR-7041) especially the *Archéologies Environnementales*
team. We thank them a lot.
# Late Antique Basilia – a fortified settlement on the cathedral hill in Basel (Switzerland). Changes in urban land use based on archaeological and geoarchaeological evidence

Christine Pümpin<fnref n="1" />, Markus Asal<fnref n="2" />, Philippe Rentzel<fnref n="1" />

## Abstract

Archaeological excavations in urban contexts are constantly confronted with complex stratigraphies where former evidence has been obliterated by continuous settlement development such as intensive construction measures and reorganisation of space. These interventions usually left only rudimentary information about prior constructions. If preserved, as in the rare case of Martinsgasse on the cathedral hill of Basel (CH), undisturbed deposits dating to Late Antiquity are overlain by thick homogenised layers. These formed during the early 4th century to the High Middle Ages by complex processes, classifying them as urban Dark Earth. In order to better understand these formation processes, conventional study of finds and features uncovered during excavation was complemented by soil micromorphological analysis. The combined study has permitted the unravelling of the historical activities, beginning with the preparation of the construction site for the fortification of the area (275/285 AD) to the demolition of buildings in Late Antiquity (300/310 AD). The overlaying urban Dark Earth could be divided into two distinct sections, differentiated by the degree of homogenisation and the interplay between human activities (e.g. dumping, levelling) and natural processes (e.g. weathering, biological activity).

**Keywords:** Cathedral hill Basel, Late Roman period, Middle Ages, Timber-framed phase, Fortification, Urban Soils, Urban Dark Earth, Soil Micromorphology

## 1. Introduction

The cathedral hill of Basel (CH) is the historical nucleus of the modern city (fig. 1, A and B). Occupied since the Bronze Age, it has been continuously settled since the late Iron Age and development has become increasingly denser since the Middle Ages. This intense settlement activity has resulted in much of the structural components of the late Roman fortification and its associated settlement layers being lost. As a consequence, no substantial statements had previously been made on the basis of stratigraphic analysis with regard to how the terrain and the buildings within the fortification were used. This changed in 2004 when a major excavation in the northern part of the late antique fortification was

carried out (Asal 2017). In an area of ca. 450 m<fnref n="2" /> next to the western slope of the cathedral hill, which had largely been untouched by medieval or modern intrusions (fig. 1, B, n° 4), the excavators discovered numerous finds and features from the earliest phases of settlement. The excavation also uncovered a stratigraphic sequence from the late Roman construction period of the fortification and from its first settlement phase of timber-framed buildings (the so-called timber-framed phase), which in places was very well preserved (fig. 2, A and B). This included deposits from a 20 to 30-year period with residential and fortification activities around AD 275/285 to the demolition of the buildings around AD 300/310. The overlying deposits ranging in date from the early 4th century to the advanced High Middle Ages, however, had been transformed by natural and anthropogenic soil processes into a layer of Dark Earth deposit difficult to read macroscopically. The use of geoarchaeological methods, particularly of large block samples and thin sections, was for the study of this layer and its interpretation an important tool. In this contribution, a

<footnote n="1">1. University of Basel Integrative Prehistory and Archaeological Science (IPAS), Spalenring 145, 4055 Basel, Switzerland, christine.puempin@unibas.ch</footnote>

<footnote n="2">2. Archaeological Service of Basel-Stadt, Petersgraben 11, 4051 Basel, Switzerland</footnote>
<figure><img src="image_6.png" /><figcaption>Figure 1: A. Basel is located on the border to Germany and France in the Upper Rhine Plain. B. The cathedral hill on today's topographic map of the city with the major features of its late Roman fortifications. The number 4 marks the 2004 excavation site. (Picture A: Swisstopo; B: Archaeological Service of Canton Basel-Stadt).</figcaption></figure>
selection of samples is presented for a better understan-
ding of the stratigraphic sequences and their formation.

## 2. Geographical and archaeological settings

Basel is situated on the southern tip of the Upper Rhine Plain (fig. 1, A), where the River Rhine bends northwards, at the crossroads of different transportation axes. The cathedral hill (fig. 1, B) in the centre of Basel is a dominant promontory, a remnant of a Pleistocene gravel terrace (Kock et al. 2009), above the Rhine. On the other side it is delimited by the Birsig valley, a local tributary of the Rhine. The late Roman fortification was erected towards the end of the 3rd century AD after the border of the Roman Empire had been pulled back to the Rhine and was part of the late antique border fortification in the northern provinces. The most important fortification remains that have come to light so far include sections of the southern and western defensive walls and a double fortification ditch on the outside of the southern wall. The buildings identified inside the fortification were used for residential, administrative and commercial purposes (Asal 2017). However, they were all only partially preserved, as were small sections of a road running south-east to north-west. Cemeteries were uncovered to the north and south of the fortification (fig. 1, B).

## 3. Materials and methods

Over the course of the excavation work, targeted block samples were taken from profiles in numerous locations throughout the excavated area. The oriented blocks measured up to 25 cm in height and 10 cm in width. They were secured using plaster bandages, impregnated with epoxy resin in the laboratory and sawn after hardening. The polished blocks allowed a detailed macroscopic assessment and correlation of the layers. Using thin sections obtained from the block samples (0.03 mm in thickness and 47 mm square), microscopic analysis was performed with a polarising microscope at a magnification of 25x to 630x in plane-polarised light (PPL) and crossed polarised light (XPL). Microscopic description followed the guidelines of Bullock *et al.* (1985), Stoops (2021) and Verrecchia and Trombino (2021). The works of Goldberg and Macphail (2006) as well as Nicosia and Stoops (2017) and Stoops (2018) were used for further identification of components and soil specific characteristics.

# 4. Results

## 4.1. The timber-framed phase

The stratigraphy of the timber-framed phase consisted of five layers that were easily distinguished macroscopically (fig. 2, B). A combination of conventional methods, such as a macroscopic layer description and archaeological analysis of the finds and features with micromorphological analyses, carried out on three blocks (M1, M3 and M8; fig. 3 and fig. 4) yielded the following results (see fig. 2, B and tab. 1):

### 4.1.1. The southern part of the site

**Levelling layer**

The bottom-most and thus earliest late Roman deposit was a levelled layer of dumped loam (fig. 3, M3 layer 3.141). Micromorphologically, this horizon was characterised by an organic, slightly calcareous loam with anthropogenic components such as microcharcoal, occasional pottery fragments and phosphatic faeces. The loam had a high humus content with granular and crumb microstructure typical of topsoil. However, there were no clear indications to suggest exposed surfaces (e.g. silt coatings) with vegetation markers. This micromorphological observation as well as the layer geometry in the field indicated that the sediment corresponded to topsoil material from the surrounding area, which had been redeposited on the edge of the slope of the plateau. The level of the terrain was thus raised by ca. 50 to 60 cm, but only after the surface humus had been removed and the terrain had been reshaped in such a way that rainwater drained from the edge of the slope towards the centre of the site thanks to the incline that had been created. Moreover, a slight north-south incline drained the water southwards into a channel (fig. 2, A), which ran it off via the western edge of the slope.

**First occupation layer with construction horizon**

The levelled layer was overlain by the first occupation surface (fig. 3, layer 3.106), a paving consisting of coarse gravel. Due to intensive construction activity, this stabilising gravel paving was covered by a multi-layered construction horizon (fig. 3, layer 3.177), which stood out micromorphologically as a strongly compacted sediment with horizontally aligned, angular stone chips of non-local limestone and sandstone, and fragments of mortar and efflorescence of gypsum (fig. 3, c). Accumulations of wood ash, charcoal and burnt clay were also observed and interpreted as waste material from hearths. Continuously occurring quartz grains with melted edges pointed to high temperatures, probably in the context of
<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

Figure 2: A. Excavated area 2004/1 with the features from the timber-framed phase and four reconstructed building units SR I ge 1 to SR I ge 4. Red line: section shown in B; black lines: geoarchaeological samples M1, M3, M8, M9 and M34. B. Section with the complete sequence of layers from the timber-framed phase (in colour) and stratigraphical synopsis. a: levelled layer; b: coarse gravel paving; c: construction horizon; d: occupation layer; e: demolition layer and f: transition layer. Red boxes: projected locations of the geoarchaeological soil samples. The upper grey layers are part of the Dark Earth deposit, the lower uncoloured layers are of Early Roman and La Tène period date. C. Picture of the profile with sample M8 and M9 showing in the lower part the timber-framed phase and in the upper part the Dark Earth deposit (see also B). M9 is presented in dashed lines as it is only mentioned briefly in the paper. (Picture A-C: Archaeological Service of Canton Basel-Stadt).
metallurgical activities (Courty *et al.* 1989). On this activity surface, the excavation uncovered the remains of a major building site facing the western edge of the slope: a large dump of coarse masonry mortar, remnants of slaked lime, concentrations of limestone and sandstone chips from the dressing of building blocks and a small forge. The layout of the construction site and other indications suggest that this was the building site for the fortification’s western defensive wall. This was the first ever proof of the long-contested theory that there had been a defensive wall to the north of the cathedral hill as well; the theory was further supported by the water drainage system, which showed that the builders had been intent on keeping water away from the western edge of the slope in order to protect the foundations of the defensive wall from retained water and from being undercut.

## Second occupation surface and demolition layer

An occupation layer up to 10 cm thick (fig. 3, M1 and M3 layer 3.175) resulting from ca. 20 to 30 years of settlement activity was found overlying the construction level and the remains of the building site which, in turn, was overlain by an up to 60 cm thick dump of reworked daub in the south-west of the site (fig. 2, B, e). It was possible, based on the analysis of the post-holes and – in the case of two buildings - the extent of the layer of dumped daub, to reconstruct the locations of four former buildings (fig. 2, A). Two neighbouring residential and handicraft buildings constructed in timber-framing technique with wattle and daub infills were situated south of the drainage ditch near the defensive wall, whilst a wooden shelter was located north of it. Another timber-built construction stood in the middle of the site. A simple hearth made of sandstone slabs was found in front of each house; some of the hearths still contained sediment deposits with high concentrations of ash and charcoal. Distinct accumulations of small fragments of bronze vessels and evidence of hammerscale in the sediment samples attested to metalworking in this area. The central wooden building was almost certainly a bronzesmith’s workshop. In the thin sections, the dark-brown, loamy occupation layer (3.175) showed a matrix with microcharcoal and a granular and crumb microstructure. The material had probably accumulated in a presumably unsheltered backyard area, which was exposed over a relatively long period of time. This was indicated by fine slaking crusts and a detectable slight vegetation cover, which would have led to humification processes. The latter was identified based on traces of roots, earthworm granules and pellets of mesofauna. The composition of the sediment and the traces of weathering (mainly observed as alteration and decalcification process),

suggested that relatively long-lasting settlement activities took place in the immediate vicinity, attested to by the presence of domestic waste (e.g. charcoal, ash, charred macroremains and bone fragments). The presence of dung in thin sections (e.g. burnt dung, phosphate concentrations and isolated spherulites) as well as trampled areas point to the presence of animals (fig. 3, b). Craft working in the immediate vicinity is attested to by metal slag and molten quartz grains. From a geoarchaeological point of view, the clear upper margin of the layer marked a hiatus or at least a phase of much reduced accumulation. Without clear archaeological evidence, it cannot be concluded that this observation represents a settlement hiatus at the end of this phase. However, it indicates a change in the use of the area after the demolition of the timber-framed buildings.

The excellent preservation of this presumed courtyard area was due to a rapid covering with demolition rubble from the timber-framed buildings (fig. 3, layer 3.043b). The original construction material bore a fine sandy-loamy composition and was probably extracted from the St Alban Valley, an alluvial plain, approximately one kilometre east of the cathedral hill. The lower terrace of the River Rhine is covered by such silty-sandy floodplain deposits (Matt 2007, Kock *et al.* 2009), which is suited well for daub fabrication (van Ossel and Brunet-Villatte 1998, Deschler-Erb and Richner 2013). Interestingly, the thin sections from the upper part of the demolition rubble (fig. 3, M1 layer 3.043a) showed zones with hearths, traces of trampling and activity areas.

The latter suggested that the loam was levelled all at once and that the subsequent activities only took place on the top surface of the demolition layer. Sediment compaction, charcoal flecks and trampled gravel, together with phosphatic faecal remnants attested to an activity surface (fig. 3a). From a micro-morphological point of view, the dumped daub shows no signs of weathering, homogenisation or humification. Therefore, it is quite probable that this surface was semi-covered or covered by a roof (Banerjea *et al.* 2015, Rentzel *et al.* 2017).

### 4.1.2. The northern part of the site

A similar sequence, as previously described, could be captured in the northern part of the site (M8, fig. 2, C and fig. 4). Overlying the coarse gravel paving (layer 1.054) known from the southern section of the excavated area (cf. fig. 3 and 2, B; layer 3.106) was a late Roman layer of gravel (layer 1.109b), which contained chips of building blocks and mortar fragments redeposited from the construction site located further to the south (layer 3.177). Compacted areas
of gravel surrounded by a bioturbated fine sediment containing charcoal, indicated settlement activities.

An organic, homogeneous occupation layer (layer 1.109a) had accumulated on top of this gravel. Under the microscope, it was a compact fine sediment overprinted by trampling that contained microcharcoal, building rubble (e.g. chips of crushed tile mortar and fragments of daub), waste from craft working (e.g. siliceous slag and quartz with melted edges) and highly fragmented phosphatic faeces. The latter, identified as deriving from omnivores or carnivores (Brönnimann et al. 2017), bore markers for hydro-morphic conditions (neoformation of vivianite, fig. 4, d), pointing to a waterlogged and wet environment in a phosphate rich surrounding (McGodwan and Prangnell 2006). Dung spherulites and phytoliths provided indications regarding the provenance of a high proportion of weathered organic material originating from decayed ruminant dung (Shahack-Gross 2011). Rough pebbles, burnt rocks and chips of building rubble sealed off the level.

The micromorphological observations point to a late Roman occupation layer, representing an outdoor area such as a square or a courtyard, where domestic animals were kept. This area was levelled and paved with construction rubble, probably due to demolition works.

## 4.2. Dark Earth

Over the centuries a layer of up to two metres in thickness formed above the levelled demolition layer from the timber-framed phase (fig. 2, B, e) and, where it was not present, above the transition layer (fig. 2, B, f) or the occupation layer (fig. 2, B, d). Whilst some of the material came from later phases of use, some of it was older and had been redeposited in levelled areas or in the fills of early medieval pit dwellings. Due to its severely homogenised fabric, this material, which covered the entire period from the end of the timber-framed phase (early 4th century) to the advanced stages of the High Middle Ages, could not be macroscopically divided into individual layers with any degree of certainty.

Significant material homogenisation and a resulting lack of macroscopically identifiable stratification are features typical of urban Dark Earth, a phenomenon that is regularly encountered in late antique and medieval strata. Thanks to the seminal work of Richard Macphail (1981) on Dark Earth in England and the ongoing studies in European cities concerning this topic (e.g. Nicosia et al. 2017, Borderie et al. 2021), today we better understand the transformation processes resulting in the homogenisation of the soil. The transformation involves among other natural

processes such as weathering, biological activities, soil formation and natural sedimentation. Different anthropogenic activities such as soil extraction, cultivation, introduction and redeposition of material likewise play an important role and lead to the transformation of initially well stratified deposits into fine-grained and macroscopically unstratified material (Nicosia et al. 2017).

In order to gain as much information as possible about the original stratigraphic situation in the Dark Earth deposit presented here, a section of the excavated area was selected, which would allow us to apply the most promising combination of conventional analysis methods and geoarchaeological approaches (Asal 2017). The zone selected contained the remains of two pit dwellings, which were visible within the Dark Earth, both in section and in plan, and yielded initial indications of probable occupation surfaces when analysed macroscopically. The Dark Earth in the area in question was removed in fine spits of just 10 cm thickness. This meant that the finds recovered could be more or less reliably associated with any individual layers that would subsequently be identified, which in turn, would allow us to roughly date the stratigraphic sequence. In addition, a series of block samples were taken from one of the profiles in the selected zone, which covered the entire period from the occupation layer of the timber-framed phase to the medieval strata. Thin sections from these samples provided further information in relation to the composition and formation of the layers.

### 4.2.1. The lower section of the Dark Earth deposit – the late Roman layers

Employing conventional methods of analysing finds and features, several levels that represented probable activity surfaces were identified within the Dark Earth deposit and roughly dated. In this way, an up to 20 cm thick layer (fig. 2, B, f) directly overlying the occupation layer (fig. 2, B, d) was identified in the areas without the daub deposit from the timber-framed phase. It dated from the late Roman period after the timber-framed phase (4th/5th centuries) but could not be further subdivided macroscopically nor were there any indications concerning its function. It marked the transition between the well stratified layers of the timber-framed phase and the Dark Earth (“transition layer”). In the following paragraphs, the geoarchaeological results (see M8 fig. 4 and tab. 1) representing the lower section of this deposit are presented in stratigraphic sequence.

**_The "transition layer"_**

A homogeneous layer (1.097) of 20 cm in thickness overlying the occupation layer (1.109a) and containing
Sample M1 & M3 Late Roman construction site overlain by organic rich occupation layers and dumped daub

<figure><img src="image_9.png" /></figure>

Figure 3: Polished section of samples M1 and M3. Red bars indicate the position of the thin sections (TS). Microphotographs of the layers are shown on the right hand side. a. TS M1.1: The upper edge of the dumped loam from timbered-framed houses is compacted and shows signs of trampling (red arrows). b. TS M3.2: Occupation layer with remains of dumped dung comprising many phytoliths (lower part of the picture). Besides ash concentrations (green arrows), calcium-oxalates (red arrow) originating from plants and spherulites (yellow arrow) have also been preserved. c. TS M3.3: Deposits from the late Roman building site with sandy, calcareous loam. Ash concentrations, fragmented phosphatic coprolites (C), mortar remains (M) and a rosette-like efflorescence of gypsum crystals (yellow arrow) are discernible.
significant proportions of mortar fragments and læss-based daub, was divided into at least four distinct layers (1.097a-d; fig. 2, B and fig. 4). In the thin sections, this stratum was characterised by a high amount of decayed organic matter, represented by many isolated phytoliths. Further, the presence of chrysophytes (golden algae) and diatoms was also notable (Verleyen *et al.* 2017). Occasionally, sharp-edged and rounded soil aggregates, probably cut marks, were observed in this layer (pers. comm. Y. Devos 28.11.11).

The base of the lowest section (1.097d), which measured approximately 5 cm in thickness, was characterised by a charcoal-rich fine sediment with diffuse gravelly areas. It was interpreted as an occupation layer with the presence of animals being attested to by phosphatic coprolites. Construction rubble and settlement waste also accumulated during this settlement phase. Besides tile fragments and weathered masonry mortar, daub in the form of læss loam was also present. It increased towards the upper boundary of the layer and was clearly distinct from the sandy daub of the timber-framed phase (fig. 3, layer 3.043b). The components can be classified as material from the demolition of stone-built or timber-framed houses brought in from the surrounding area. This marks the beginning of a change in the type of construction used in the environment of the excavated area on the cathedral hill in Basel, in that stone buildings were beginning to replace the timber-framed houses. Moreover, the sediment contained typical signs of water saturation (e.g. vivianite), which pointed to periodically marshy conditions. Earthworm granules with early signs of decalcification and the level of homogenisation due to bioturbation pointed to a rather lengthy phase of sedimentation (Goldberg and Macphail 2006).

The thin sections showed a level of fine gravel (1.097c) overlying this layer with a slightly higher aggregated groundmass. It contained decayed construction rubble and mortar remnants, as well as lumps of læss-based daub (fig. 4, c). The deposit contained high levels of decayed organic matter, which included remnants of weathered dung (spherulites and phytoliths). We can assume that the gravel was brought into the area to stabilise the occupation surface in the marshy terrain.

Continuous use of the site subsequently led to the accumulation of a deposit (1.097b) measuring just over 7 cm in thickness with a significant amount of building rubble (e.g. crushed tile mortar and fragments of tufa) and læss-based daub, which; however, was highly fragmented, mixed and weathered. Considerably sized lumps of slag indicated that craft working had taken place. Phosphatic coprolites point to animal husbandry or latrine waste. Additionally, the presence of dusty silt coatings increases significantly. This

part of the site was interpreted as an open space area, which had been homogenised by human activities and natural processes (e.g. bioturbation, weathering).

The uppermost part of this deposit (1.097a, see M9 fig. 2, B and C) shows a slightly decalcified homogenous deposit with little organic matter but with a high proportion of finely dispersed microcharcoal and decayed building rubble (e.g. mortar fragments, weathered daub, chips of building blocks). Slightly compacted areas with silty crusts suggested the presence of former occupation surfaces, though it was not possible, due to the state of preservation, to pinpoint individual trampled surfaces. Weathered earthworm granules and pellets of enchytraeids (Davidson *et al.* 2002) showed that this layer was a topsoil deposit, which had been repeatedly reworked by soil fauna. This resulted in a high fragmentation of the nutrient-rich components (e.g. charcoal and coprolites) and a higher porosity of the deposit. In summary, layer 1.097a was interpreted as a levelled deposit of dumped construction rubble with a slow accumulation and spreading of organic matter on a non-constructed surface, i.e. in an outdoor area. Human activities and bioturbation, by soil fauna, had mixed and homogenised the sediment in this proposed outdoor area and transformed it into Dark Earth.

### 4.2.2. The upper section of the Dark Earth deposit – the early and high medieval layers

An early medieval occupation surface was identified based on the level from where the pit dwellings had been dug, and dated to the Merovingian period (7th/8th centuries). Another occupation surface dating from the 8th/9th centuries was identified on the basis of hearths and stone settings. This early medieval surface micromorphologically was examined more detailed (fig. 4, M34 and tab. 1), revealing different occupation layers, which are presented as follows:

**Occupation layers**

The state of preservation of layer 1.464, a homogenous and humiferous sediment of sandy loam rich in microcharcoal, was classified as moderate. Some of the components (e.g. phosphatic coprolites) were severely weathered or, like the organic matter, much decayed. Weathered gravel, fragments of mortar and chips of building stones occurred repeatedly and attested to construction and demolition work that had taken place in the surroundings of the excavated area. The sediment was strongly homogenised by soil fauna activity leaving behind a dominant content of excremental aggregates. There was also clear evidence of slaking crusts and dusty silt coating, which pointed to a surface that had been exposed to the elements and supported the macroscopic interpretation as an occupation surface (fig. 4, b).
<figure><img src="image_10.png" /></figure>

Figure 4: Polished section of samples M8 and M34. Red bars indicate the position of the thin sections (TS). Microphotographs of the layers are shown on the right hand side. a. TS M34.1: Heavily burnt læss (L) and weathered earthworm granule (red arrow) are present in the Dark Earth layer. b. TS M34.3: Bioturbated Dark Earth layer with well preserved, compacted silty crust (red arrows) indicating an exposed surface (outdoor area). c. TS M8.2: Læss with clay coatings (red arrows) point to the presence of altered daub. d. TS M8.3: Homogeneous, occupation layer with weathered organic material (brown areas), charcoal (ch) and precipitation of vivianite (V).
<table><thead><tr><td>Layer</td><td>Layer composition</td><td>Microstructure</td><td>Organic elements</td><td>Anthropogenic elements</td><td>Pedofeatures</td><td>Related figures</td></tr></thead><tbody><tr><td>1.104</td><td>Homogeneous, microcharcoal rich sandy loam with few gravel</td><td>Channel, chamber, granular and locally angular blocky</td><td>Slightly humic; decayed organic matter; few phytoliths, chrysophytes</td><td>Mortar, tile chips, charcoal, phosphatic coprolites, mortar, bones, ceramic, eggshell</td><td>Slacking crust, vivianite</td><td>Fig. 4, Fig. 4, a</td></tr><tr><td>1.228</td><td>Homogeneous, microcharcoal rich sandy loam with few gravel</td><td>Channel, chamber, granular and locally massive and angular blocky</td><td>Slightly humic; decayed organic matter; few phytoliths, chrysophytes</td><td>Mortar, tile chips, charcoal, (un)burnt daub, bones, ceramic, eggshell</td><td>Slacking crust</td><td>Fig. 4</td></tr><tr><td>1.464</td><td>Homogeneous, microcharcoal rich sandy loam with few gravel</td><td>Channel, chamber, granular</td><td>Slightly humic; decayed organic matter; phytoliths, few chrysophytes</td><td>Mortar, building stone chips, burnt daub, phosphatic coprolites, bones, ceramic, charcoal</td><td>Slacking crust, dusty silt coating</td><td>Fig. 4, Fig. 4, b</td></tr></tbody></table>

<table><tbody><tr><td>1.097a</td><td>Homogeneous, microcharcoal rich sandy loam</td><td>Channel, chamber, locally massive</td><td>Low concentration of organic matter</td><td>Mortar, daub, building stone chips, charcoal, phosphatic coprolites, bones</td><td>Silty crust</td><td>Fig. 2B</td></tr><tr><td>1.097b</td><td>Homogeneous, microcharcoal rich sandy loam</td><td>Granular, channel, chamber</td><td>High concentration of decayed organic matter, phytoliths, chrysophytes, diatoms</td><td>(Un)burnt læss daub, mortar, tile chips, tufa, slags, charcoal, phosphatic coprolites, bones</td><td>Dusty silt coatings, vivianite</td><td>Fig. 4</td></tr><tr><td>1.097c</td><td>Microcharcoal rich loamy gravel</td><td>Channel, chamber, granular</td><td>High concentration of decayed organic matter, phytoliths, chrysophytes, diatoms</td><td>Mortar, (un)burnt læss daub, charcoal, ceramic, dung spherulites</td><td>Vivianite</td><td>Fig. 4, Fig. 4, c</td></tr><tr><td>1.097d</td><td>Microcharcoal rich loam</td><td>Channel, chamber, granular</td><td>High concentration of decayed organic matter, phytoliths, chrysophytes, diatoms</td><td>Mortar, tile chips, burnt læss daub, charcoal, phosphatic coprolites, bones, ceramic</td><td>Vivianite</td><td>Fig. 4</td></tr><tr><td>1.109a</td><td>Microcharcoal rich loam with gravel on top</td><td>Channel, chamber, slightly granular</td><td>Decayed organic matter, few phytoliths, chrysophytes, rare diatoms</td><td>Charcoal, phosphatic coprolites, dung spherulites, daub, mortar, molten quartz</td><td>Vivianite</td><td>Fig. 4, Fig. 4, d</td></tr><tr><td>1.109b</td><td>Rhine gravel with microcharcoal rich loam</td><td>Channel, chamber</td><td>Decayed organic matter, few phytoliths, rare chrysophytes</td><td>Mortar, building stone chips, charcoal, bones</td><td></td><td>Fig. 4</td></tr><tr><td>1.054</td><td>Rhine gravel from C-Horizon</td><td>no TS</td><td>no TS</td><td>no TS</td><td>no TS</td><td>Fig. 4</td></tr></tbody></table>
<table><caption>Table 1: Main micromorphological characteristics of the studied layers of the Martinsgasse. TS = thin section.</caption><thead><tr><td>Layer</td><td>Layer composition</td><td>Microstructure</td><td>Organic elements</td><td>Anthropogenic elements</td><td>Pedofeatures</td><td>Related figures</td></tr></thead><tbody><tr><td>3.043a</td><td>Microcharcoal rich, fine sandy loam with few gravel</td><td>Massive, locally slightly micro-laminated</td><td>Low concentration of decayed organic matter, few phytoliths, rare chrysophytes</td><td>Charcoal, daub, phosphatic coprolite, bones</td><td></td><td>Fig. 3, Fig. 3, a</td></tr><tr><td>3.043b</td><td>Slightly loamy, fine sand, material from C- and Br-Horizon and fluvial deposit</td><td>Massive, locally micro-laminated</td><td>Low concentration of decayed organic matter, few phytoliths, rare chrysophytes</td><td>Daub, tile chips, charcoal, bones, fish scale, ceramic</td><td></td><td>Fig. 3, Fig. 3, a</td></tr><tr><td>3.175</td><td>Microcharcoal rich slightly loamy gravel</td><td>Channel, chamber, locally microaggregated and slightly microlaminated</td><td>Slightly humic, decayed organic matter, few phytoliths, chrysophytes, rare diatoms</td><td>Charcoal, wood ash, charred microremains, bones, fish scales, mortar, dung, dung spherulites, slags, molten quartz, iron object</td><td>Slacking crust, phosphatic pedofeatures</td><td>Fig. 3, Fig. 3, b</td></tr><tr><td>3.177</td><td>Sandy silty loam</td><td>Massive, microlaminated</td><td>Burnt organic matter, few phytoliths and chrysophytes</td><td>Building stone chips, gypsum efflorescence and mortar fragments, wood ash, charcoal, burnt clay, burnt dung, molten quartz</td><td></td><td>Fig. 3, Fig. 3, c</td></tr><tr><td>3.106</td><td>Rhine gravel from C-Horizon</td><td>Massive, locally micro-laminated</td><td>Decayed organic matter, few phytoliths and chrysophytes</td><td>Burnt daub, charcoal, phosphatic coprolite, bones</td><td></td><td>Fig. 3</td></tr><tr><td>3.141</td><td>Microcharcoal rich, slightly calcareous, humic loam with some gravels</td><td>Channel, chamber, granular, crumb</td><td>Decayed organic matter, humic, few phytoliths</td><td>Phosphatic coprolites, ceramic, bones, (un)burnt loam</td><td></td><td>Fig. 3</td></tr></tbody></table>
The base of the next upper layer 1.228 had a slightly higher gravel content. The sediment was generally composed of a sandy loam, which was in some areas compacted. The fine components consisted of microcharcoal and severely degraded organic matter. Fine chips of tiles, fragments of mortar, eggshells, rounded pieces of charcoal, bone and pottery all attested to settlement activity. The presence of gravel and building rubble at the base of the layer could point to the introduction of a deposit to stabilise the surface. The signs of weathering were slightly stronger than in the underlying levels. This was clearly noticeable, particularly due to the presence of severely corroded limestone from gravel and earthworm granules. It is possible that the sediment was modified by a sedimentation hiatus, i.e. a phase of weathering and humification (due to a vegetation cover?).

The bottom edge of the next layer 1.104 consisted of horizontally aligned gravel with many burnt components and probably represented an activity area. The composition of the deposit was the same as that of underlying layer 1.228. However, the traces of weathering on the calcareous components were more pronounced here and there was no calcium carbonate in the fine fraction (fig. 4, a). This level was characterised by a significant degree of homogeneity, clear traces of weathering and a high level of bioturbation in the upper sections of the layer, which is typical of Dark Earth deposits.

# 5. Interpretation and discussion

## 5.1. The timber-framed phase

Using the layers of the timber-framed phase as an example, the preceding remarks showed how micromorphological analyses are an important complement to discuss conventionally elaborated layer interpretations, in order to support and refine them with new questions and different results. This is illustrated by the following examples:

a. The micromorphological examination of the lower part of the timber-framed phase mainly revealed a dumped layer that had been introduced prior to construction work on the defensive wall (fig. 3, M3 layer 3.141). Its structure was typical of a humiferous topsoil deposit. It can be classified as redeposited material and can hypothetically be viewed as indirect evidence of the existence of undeveloped settlement areas with a humiferous horizon on the cathedral hill in the Middle Imperial period shortly before AD 270/280. This result underpins previous insight concerning the size of the preceding

Middle Imperial settlement on the cathedral hill of Basel, which suggested that only the southern area of the hill had been developed during that period. Of course, this does not mean that the northern half of the hill was not used in the Middle Imperial period, but the evidence seems to point to extensive and rather ephemeral types of land use such as animal husbandry, gardening or simple crafts with light construction. The notion of these types of land use can be reconciled with the presence of humiferous topsoil.

b. Analysis of a multi-layered deposit (fig. 3, layer 3.177), which had formed during construction of the defensive wall, also included one of several concentrations of chips of building blocks found at the building site. Rock analysis revealed that none of the building blocks were local (Rentzel 1998). The thickness of this stone chip layer was relatively moderate at ca. 5 cm, given the size of the building site identified. Similar layers uncovered at other sites, for instance at nearby Colonia Augusta Raurica (CH), e.g., at the theatre, were considerably thicker, measuring up to 10 cm (Rentzel 2009). The stones of the defensive wall in Basel were reused blocks and therefore required very little dressing. This would explain not only the thinness of the stone chip layer but also the heterogeneous petrographic range. The theory is further underpinned by the fact that a secondary use of stones in the construction of the defensive wall was attested to in other areas of the cathedral hill.

c. Based on remnants of metal slag and quartz grains that had melted in high temperatures, the micromorphological analysis of the occupation layer from the timber-framed phase (fig. 3, layer 3.175) revealed that smithing had taken place in the areas around the hearths. Besides evidence for metal processing on site, micromorphological examination of the block samples also yielded numerous indications pointing to another, completely different land use. Burnt remnants of dung, phosphate concentrations, fragmented coprolites and isolated dung spherulites were also found around the hearths. This animal excrement can be explained by the presence of farm animals, which were probably kept inside the fortification. Analysis of the occupation layer also provided important clues in regards to this question. Slaking crusts and traces of trampling show that the ground surface at the time was strongly mixed and very muddy. This backyard-like occupation surface had formed in an open area that was intensively used by humans and animals.
## 5.2. Dark earth

Dark Earth deposits of up to two metres in thickness were found overlying the well stratified timber-framed phase and appeared very homogeneous and poorly stratified. Using conventional methods of layer analysis, several settlement horizons dating from the 4th century to the High Middle Ages were identified within this unit of deposits but could not be subdivided any further or interpreted in terms of function. Further subdivisions were, however, identified by means of micromorphological analyses carried out on block samples taken from the unit of layers and insight was, indeed, gained in terms of their functional interpretation and their subsequent homogenisation processes:

a. After demolition of the timber-framed houses, a deposit formed either above the demolition layer, or where this was not present, directly above the occupation layer of the timber-framed phase. This deposit was approximately 20 cm thick and could not be subdivided any further by macroscopic means (fig. 4, layer 1.097). Micromorphological analysis showed that this Dark Earth unit consisted of at least four layers overlying each other (fig. 4, M8 layer 1.097a-d). An occupation layer with an abundance of redeposited demolition rubble from stone-built constructions (masonry mortar, tile fragments) and with evidence of the presence of animals was overlain by a gravel level with degraded building rubble and dung markers, which was interpreted as an occupation layer for the purpose of stabilising the ground. A further occupation layer had accumulated on top of it, which again contained a lot of rubble from stone-built houses and evidence of animal husbandry. The fourth stratum identified was a layer of topsoil consisting of redeposited building rubble mixed with organic matter, which was strongly reworked and muddied by trampling. Breaking down this macroscopically inaccessible unit of material into at least four layers and analysing their composition allowed us to draw concrete conclusions in terms of layer formation and of how the area at the Martinsgasse was used during the period immediately following the abandonment of the timber-framed houses. Apparently the area continued to be undeveloped and the unfortified terrain became silted up as a result of its exposure to the elements, but mainly due to continuous use by both humans and animals. It could be shown that animals continued to be kept in the near area even after demolition of the timber-framed buildings and there was a complete lack of evidence of any new development. There were, however, repeated attempts to fortify parts

of the site by introducing gravel deposits or levelled building rubble.

b. Micromorphological analyses of layer 1.097 yielded a high concentration of diatoms and chrysophytes. These types of algae, especially the chrysophytes, live in bodies of water, but can also form in large puddles that exist over several weeks. The layer studied, however, did not exhibit any deposits typically formed in water, making it seem unlikely that the algae had come from large natural puddles in the excavated area. Nor would the algae have been introduced to the site in association with the fluvial daub because neither diatoms nor chrysophytes have so far been identified in any of the Roman period layers that consisted solely of daub. As diatoms are also found in terrestrial conditions, their frequent occurrence in this layer, together with the chrysophytes (tab. 1), postulate that they did not live onsite. The high amount found in this layer raises the question if these algae were introduced into the area by irrigation and not by animal dung (Shahack-Gross 2011). One observation made in the centre of the excavation, on a large layer of mortar in the construction horizon (3.177), was interesting in this respect: several groups of parallel grooves were found overlying each other and running in different directions. They can be compared to very similar features uncovered at London, Whittington Avenue (Macphail 1994) and have been interpreted as the lowest preserved evidence of seed furrows, which had been dug by hand using a spade. Here, too, the micromorphological examinations provided interesting results. Probable cut marks were found in some areas of the thin sections, which may have resulted from the use of a plough, spade or similar tool (Devos et al. 2011, Deák et al. 2017). Further, the high number of isolated phytoliths and phosphatic coprolites can also point towards horticulture practices (e.g. decomposed cereal remains, manure, Devos et al. 2022). The study of the archaeological features combined with the micromorphological analyses, therefore, provided clear evidence not only of the fact that animals had been kept in the area but that it had probably also been used sporadically for small-scale cultivation.

c. As shown above, the thin sections from the lower post-timber-framed layers in the Dark Earth deposit repeatedly yielded evidence of muddy occupation surfaces and of water saturation. This suggests that rainwater did not drain off sufficiently well. This finding is consistent with the discovery during the excavation of a drainage channel dating from the timber-framed phase, which ensured that rainwater drained off via the western edge of the slope. From
<figure><img src="image_11.png" /></figure>

Figure 5: The late antique fortification on the cathedral hill of Basel (view to the north). The reconstruction shows the location with its openly settled northern part, with room for animal husbandry and gardening, the southern part with dense housing and the *Suburbium* outside the southern fortification wall. For information on the structures, see also fig. 1. (Picture: Archaeological Service of Canton Basel-Stadt, T23835, basis Jonas Christen; Marco Bernasconi, archaeolab.ch).

the end of the timber-framed phase onwards, this drainage channel had been backfilled with demolition rubble from the timber-framed houses and thus, became defunct. As a consequence, rainwater subsequently remained in or on the topsoil for significant periods of time, thus, causing the ground to become marshy. The process also promoted vegetation growth on the surface and the formation of a rich soil fauna, which made a significant contribution to the development of Dark Earth.

d. The formation of the Dark Earth in the Martingasse is the result of an interplay between natural processes and human activities. The latter was mainly characterised by dumping and levelling of gravel and construction rubble leading to the accumulation of sediments. Soil interventions (cultivation, extraction) and the occupation with muddy open spaces, further homogenised these layers. Weathering and biological activities have become more important with the onset of the transition layer and increase significantly in the upper section of the Dark Earth. This could be related to the fact that an input of different waste sources and levelling material slows down or decreases over time promoting natural processes. Despite the strong homogenisation processes, the continuous presence of animals and humans in this area is still visible in the Dark Earth.

## 6. Conclusion

The results of the micromorphological studies provided new insight, resulting in significant changes to previous evaluations on what the fortifications on the cathedral hill would have looked like. Analysis of the stone chips found at the building site, which attested to the work of stonemasons, provided various indications that suggested that they were remnants from the dressing of stone blocks for the purpose of reusing them in the construction of the defensive wall. Moreover, block samples from the vicinity of the hearths supported the assumption that the area had been used for metal processing during the timber-framed phase. However, our image of how the area was used has changed considerably. The evidence of domestic animals and probable agricultural activities within the defensive walls on the cathedral hill has consequences beyond the interpretation of the occupation layer itself, since it shows that urban, military and rural land uses (e.g. animal husbandry, small-scale cultivation) all co-existed within the late Roman fortification on the cathedral hill in Basel (fig. 5). It also raises the question as to whether and to what extent rural forms of land use were a characteristic feature of late Roman fortified settlements in general (see also Wouters et al. 2019). Furthermore, it shows that there was obviously enough space within the fortification on the cathedral hill for
such activities. Overall, however, it paints a picture of a late Roman fortified settlement landscape that requires further discussion amongst researchers. Such sites were obviously more than cramped urban centres that were completely dependent on the hinterland for agricultural produce, but settlements that could be quite sparsely populated, with an almost rural character, and be partially self-sustaining, serving both rural and urban needs.

Micromorphology allowed the identification of several occupation surfaces within the bottommost section of the Dark Earth deposit, which immediately followed the timber-framed phase and dated from the early 4th to 6th centuries AD. It is not possible to ascertain from the samples whether these were large-scale areas or whether they were concentrated in rather small sections of the site. It is, however, worth noting that rural land use was proved for these occupation surfaces too. Demolition of the timber-framed houses and abandonment of the drainage ditch from the timber-framed phase, which subsequently resulted in water saturation and silting represented a change in the use of the site from a residential area, which was also used for craft working and farming, to a land use that was even more agrarian in nature.

## Acknowledgements

We are grateful to the Archaeological Service of Canton Basel-Stadt, the Integrative Prehistory and Archaeological Science (IPAS) at the University of Basel and the WEAVE-Project "Welcome to the Dark Side - disclosing the invisible stages of medieval urbanisation through the integrated study of European Dark Earths" (SNSF grant No. 205278) for making the records and finds from the excavation available to us and for providing funding and staff for the preparation of this paper. We would like to thank A. Hagendorn, Y. Devos and R. Macphail for invaluable inputs. Our thanks also go to A. Niederhäuser for his diligence in editing the manuscript and to P. von Holzen for the processing of the images. Our final thanks goes to Sandy Hämmerle for the professional translation of our text, the anonymous reviewers for their constructive comments and suggestions, and the proofreader for the final correction of our manuscript.

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