# Earthen architecture on archaeological sites: sustainability principles vs decay processes

David Gandreau, Chamsia Sadozaï, Sébastien Moriset

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David Gandreau, Chamsia Sadozaï, Sébastien Moriset. Earthen architecture on archaeological sites: sustainability principles vs decay processes. XVIII UISPP World Congress (4-9 June 2018, Paris, France), Jun 2018, Paris, France. pp.5-14. hal-04021704

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Chapter 1

Earthen architecture on archaeological sites:
sustainability principles vs decay processes

David Gandreau

gandreaudavid@hotmail.com, corresponding author

Chamsia Sadozaï

ch.sadozai@gmail.com

Sébastien Moriset

sebastien.moriset@grenoble.archi.fr

Laboratoire CRAterre, Unité de recherche AE&CC

Ecole Nationale Supérieure d'Architecture de Grenoble

Abstract

This article highlights the sustainability of earthen architecture as revealed by many archeological sites. Despite millennia
of slow deterioration processes, remarkably well-preserved sites have become sources of information and inspiration for
contemporary designers because of the sustainability principles they reveal. The present quest for more sustainable
ways of building will not find answers in sophisticated building techniques, but rather in what our ancestors have kept
doing for centuries: building simply with the resources at hand, such as earth. But this requires close collaboration
between archeologists and architects to bridge the 11 000 years gap that separates us from the first builders, from whom
we can still learn a lot.

**Keywords:** Earthen construction, durability, degradation, conservation, site presentation

Résumé

Cet article met en évidence la durabilité des architectures de terre révélée par de nombreux sites archéologiques. Malgré des millénaires de processus de détérioration lente, des sites remarquablement bien préservés sont devenus des sources d'informations et d'inspiration pour les concepteurs contemporains en raison des principes de durabilité qu'ils révèlent. La recherche actuelle de moyens de construction plus durables coïncide entièrement avec ce que nos ancêtres ont toujours fait: construire simplement et avec les ressources disponibles, comme le permet la terre crue. Pour cela, il est nécessaire d'établir une étroite collaboration entre archéologues et architectes pour combler le fossé des 11 000 ans qui nous sépare des premiers constructeurs, dont nous pouvons réellement beaucoup nous inspirer.

Mots-clés: construction en terre, durabilité, dégradation, conservation, mise en valeur du site

Introduction

From their emergence at least eleven millennia ago to contemporary times, the diverse constructive
cultures associated with earthen materials have continuously spread throughout the world (Figure
1). As a result, archaeological sites presenting earth as a building material for walls, floors or roofs,
are innumerable.

Some pre/protohistoric sites, still remarkably well preserved, provide the proof that earthen
construction can be perfectly sustainable under certain conditions. But in many cases, with
the departure of the inhabitants who maintained them, processes of degradation began which
gradually led to their ruin and sometimes even their almost total disappearance (Gandreau 2017:
23-30).

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<figure><img src="image_5.png" /></figure>
<figure><img src="image_6.png" /><figcaption>Figure 1. Timeline of earthen architecture testimonies © Inclusit Design 2016</figcaption></figure>

Through several examples of Near and Middle Eastern, Mediterrean and Egyptian sites built with earth, this article aims to highlight some long-lasting principles of sustainability of earthen architecture, while underlining the circumstances and processes of decay that threaten them in archaeological context.

## 2 Question of definition

'Clay', 'mud', 'earth', 'soil', 'pisé', these terms are often used by archaeologists to characterize the structures they excavate. In fact, five principal modes of implementation, namely wattle and daub, cob, mudbrick, rammed earth, and earth renders, come in many variations, that are not always easy to distinguish in archaeological context (Houben and Guillaud 1989; Fontaine and Anger 2009). To avoid any semantic confusion, we define these main techniques as follows:

- Wattle and Daub. The building skeleton is made of wood and filled up with a woven lattice of wooden strips, then covered by an earthen mix on each side (Figure 2). Examples of this technique, made of reed instead of wood, are supposed to be the earliest human constructions. The site of Dikili Tash in Greece has evidences of wattle and daub from the Neolithic period - fifth millennium BCE (see Bacoup and Prévost-Markar, this volume).

- Cob. A wet earthen mix is laid directly on the floor in thick successive layers and the sides are cut to shape a wall (Figure 3). The wall is load-bearing by itself like a monolith. This technique can be compared to hand molded pottery with coils. Examples of cob dwellings are known in Armenia since the Neolithic period (sixth millennium BCE), in the Ararat plain (Aknashen-Khaturnakh).

- Adobe or mudbrick. A wet earthen mix is molded and sun dried to create small standard elements easy to handle (Figure 4). It has been the most widespread building system in the world for centuries. The best-known example is coming from Pre-Pottery Neolithic A (eighth millennium BCE) of the famous site of Jericho (Tell es-Sultan).

- Rammed earth. Earth is compacted in a very low humid state between two pieces of wood (Figure 5). Like cob walls, rammed earth walls are monolithic. Early evidences are scarce but some examples can be found in China.

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<figure><img src="image_8.png" /><figcaption>Figure 2. Wattle and daub process © M.-N. Baudrand 2016</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Figure 3. Cob process © M.-N. Baudrand 2016</figcaption></figure>

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<figure><img src="image_11.png" /><figcaption>Figure 4. Mudbrick process © M.-N. Baudrand 2016</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Figure 5. Rammed earth process © M.-N. Baudrand 2016</figcaption></figure>

- Renders. Thin coats of earth preparation are applied on a vertical surface and can receive any type of decoration (Figure 6). Examples in Djade al-Mughara in Syria are attested since the ninth millennium BCE.

### 3 Sustainability principles

The principles of sustainability were certainly not a topic of discussion 11 000 years ago. Yet the architecture of archaeological sites teaches us real lessons of sustainability for many reasons.

The first lesson of sustainability is respect for nature. These architectures have passed through the centuries without leaving any pollution behind them, because they are made of natural materials that the construction sites provided. Earth for example was used raw; it was rarely burnt, which saved energy and ensured an impact-free return of materials to the ground.

The availability of the material, in a huge quantity with minimum transport costs, exactly under the feet of the builders, allowed the inhabitants of the past to conceive towns for several thousand people. The concept of city was born, with its large-scale vision, and was replicated for many generations thanks to the reversibility of the earthen material. The vertical stratigraphy, the fact that several occupation horizons are one on top of the other during centuries, was possible because it was easy to destroy and level old phases and re-use the same building material for the next, as it did not lose its properties. Many examples of piled-up cities are known, such as Suse in Iran which was occupied from the fifth millennium BCE until the fifteenth century CE (Amiet 1988). On a smaller scale, Ulug Depe in Turkmenistan is the only site in the region with a continuous

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<figure><img src="image_14.png" /><figcaption>Figure 6. Mural painting of Djade el Mughara. © Mission archéologique de Dja'de, E. Coqueugniot</figcaption></figure>

occupation from the Chalcolithic period until the end of the Iron Age (Lecomte et al. 2002), with more than 35 m of archaeological levels.

Another remarkable feature that is sometimes possible to appreciate for several millennia after the construction is the bioclimatic quality of these architectures, which avoid extreme heat or cold. The thermal inertia properties of the earth allow a slow restitution of the temperature within the walls if they are homogeneous and thick enough. Combined with a proper orientation, an adequate location on the site, and an appropriate ventilation system, these features provided comfort despite the absence of active heating/cooling devices.

Another characteristic is the sobriety of the means mobilised. Building was done with simple tools (hoes, wooden molds) with the only energy sources available: human (and sometimes animal) for the preparation and implementation of materials and solar for drying them. This did not prevent the production of remarkable masterpieces in terms of architectural quality and decoration. Many monumental buildings are attested, such as palaces, temples, even pyramids. Indeed, a massive ziggurat was discovered in Tchoga Zanbil for the Elamite period (third millennium BCE) in Iran, comparable to the stone pyramids of Egypt. Another noticeable building is the Great Kyz Kala in Merv, in Turkmenistan, which is supposed to be a fortified house with gigantic crenulations all built in mudbricks. This building crossed the centuries and still stands up 12 m above the ground on the Bactriana plain (Figure 7).

<figure><img src="image_15.png" /><figcaption>Figure 7. The Great Kyz Kala in Ancient Merv (Turkmenistan) ©CRAterre_D. Gandreau 2015</figcaption></figure>

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Because of the simplicity of the materials and the means of implementation, these architectures were easy to maintain with the same resources and know-how. As a result, they ensured the resilience of their inhabitants/self-builders who carried out the entire construction process, without relying on outside resources. The earthen architecture and masonry skills those people mastered are impressive lessons for us. Even in villages such as Hili 2 in the United Arab Emirates, where there is no urban settlement comparable to those of Mesopotamia, the houses of common people are still visible today 3000 years after they erected them, from the floor to almost the ceiling 2 m above the ground. The community decided to build with thin layers of cob stabilized by thin mudbricks on top of each ring, and we still don't understand the reason for it. Another example are the Ramses granaries in Egypt, called the Ramasseum, where long and narrow rooms vaulted with mudbricks are still visible today.

Let's not forget the cultural richness of the first architectures. The simplicity of the tools and materials described above have not hindered creativity. The diversity of archaeological remains that excavations have revealed are evidence of human genius to design rich and varied cultures.

## 4 Decay processes

Archaeology has revealed the full potential of earthen architecture, but unfortunately it is also participating to its loss. Indeed, two phases of decay are visible on the lifespan of earthen archaeological remains. The first one occurs when the inhabitants abandon the building, and the second one, faster, is happening after the discovery and excavations by archaeologists.

After their abandonment, all earthen buildings, regardless of the technique employed, slowly enter in a decay phase related to erosion processes. Usually, people take away reusable and precious materials such as wooden beams or stones. Absence of roof and hard material in critical points (gutter, lintel, threshold), combined to the lack of maintenance, makes the building vulnerable to wind and water deterioration (stagnation, rain, dampness), sometimes animals squat (nest, burrow, detachment on the top). Slowly but surely, soft parts are losing cohesion and sharp features are worn away creating a big mound in the landscape. After this slow-motion process, the decaying phase is over, the mound is stabilized and the buried elements easily survive for centuries, including precious decorated surfaces (Figure 8).

<figure><img src="image_17.png" /><figcaption>Figure 8. Decay processes after abandonment ©CRAterre_S. Moriset 2016</figcaption></figure>

<figure><img src="image_18.png" /></figure>
<figure><img src="image_19.png" /><figcaption>Figure 9. Open trench in Mary (Syria) left without any conservation measure ©CRAterre_M. Bendakir</figcaption></figure>

<figure><img src="image_20.png" /><figcaption>Figure 10. Undercut pathology in Ancient Merv (Turkmenistan) ©CRAterre_C. Sadozaï 2015</figcaption></figure>

When archaeologists discover a mound created by anthropic activity (also called a tepe or a tell in Middle East), a new cycle of accelerated decay is starting. Trenches are opened, walls are left exposed without roofs and trenches are dug with no way out for drainage (Figure 9).

When it is raining, water is pooling and walls are acting like sponges, absorbing all the dampness by capillarity. As a consequence, wall bases are damaged creating a weakness. This is a very common pathology, characterized by a wall profile looking like an apple core also called ‘undercut’ or ‘coving’ (Figure 10).

Other structural pathologies are observed after a long exposure without preventive conservation measures. Vertical cracks and leaning walls can, as well as the undercut, threaten the whole building's stability and can lead to a collapse. Superficial clues of degradation can also warn about the integrity of the building, such as minor cracks, material detachment or loss, and gullies (Sadozaï 2013).

Until recent times, inefficient conservation measures taken after the excavations revealed also, in some cases, major disturbances. The use of inappropriate protective materials or shelters without regular monitoring sometimes creates more damages than doing nothing (Daneels and Guerrero Baca 2015).

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# 5 Learning from earthen archaeological sites

## 5.1 Conservation

Understanding the decay processes is a key to better preserve earthen structures and possibly preserve them to future generations. Close observation of pathologies on the building and its surroundings is required to achieve a precise diagnosis (Gandreau and Sadozaï 2015). The conservation principles applied to earthen archaeological remains are well-known and are based on common sense, for example do not allow water to stagnate near the structures and impregnate the walls by capillarity, or do not leave fragile elevations exposed to wind, rain and frost without protection.

This sounds simple, but preserving an excavated site is a great challenge and can hardly be achieved once the remains are exposed. Conservation strategies need to be integrated in the archaeological campaigns, with time, financial resources and knowledgeable experts entirely dedicated to the task. Conservators should work alongside with archaeologists to apply the appropriate emergency measures required to stabilize the whole excavated sector until all the stakeholders agree upon a holistic strategy (Sadozaï and Gandreau 2016).

In theory, for any new archaeological project a conservation strategy must be thought out before starting. Many governmental authorities have understood this today and ask for realistic conservation plans to be presented before issuing excavation permits. Several archaeologists have been denied the right to dig because they could not meet the required conservation guarantees. The conservation program can of course vary depending on the findings, but it helps at least to determine in a specific time frame the appropriate conservation techniques to use, as well as the roles and responsibilities of each partner.

## 5.2 Contemporary architecture

Does it make sense to oppose these thousand years old ruined architectures versus contemporary ones? It is a trend for architects today to reconnect their contemporary production to the vernacular architecture of the region where they build. This seems logical today in a context where it has become essential to save resources by reducing the transformation and distribution circuits of building materials by using locally sourced materials and relying on the human resources of the place. This is exactly what our ancestors tried to achieve for several millennia. What we see as outdated productions of the past often appear to be extraordinary sources of inspiration for today's architects. The idea is not to duplicate ancient models, but to draw inspiration from various parameters. Which type of soil was used for which building parts? How was the soil processed and turned into buildings parts? Which tools and social organization allowed achieving building so simply and so fast? What features guaranteed thermal comfort in the absence of electricity? Many more questions can be asked. A European Union funded research programme called VERSUS (www.esg.pt/versus) listed in 2014 all the lessons that can be drawn from vernacular architecture to explore new ways to design contemporary sustainable buildings (Guillaud et al. 2014). It provides a methodology for scholars, students and professionals to easily draw the lessons from past architectures, regardless of their age, that can be reused in a contemporary way (Sanchez et al. 2018).

On an archaeological site, the link between ancient and contemporary architecture can easily be done through a site presentation strategy that requires erecting new buildings. The necessity of exhibiting artefacts in situ in a visitors' centre for example offers the possibility of building a contemporary structure with modern features inspired by ancient techniques. The project of Mari in Syria is a good example of a site museum built in earth with modern features (Figure 11).

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<figure><img src="image_23.png" /><figcaption>Figure 11. Mari Visitors' center (Syria) ©CRAterre_M. Bendakir 2010</figcaption></figure>

## 6 Conclusion

The archaeological remains of earthen constructions are rarely considered by contemporary builders as sources of information that could guide their practice. The fragility that the ruins show us immediately destroys the idea that these architectures bear lessons that have remained relevant over the millennia. However, conservation has brought many archaeologists closer to architects who are committed to contemporary issues of sustainable development, for whom the use of eco-responsible materials such as earth is obvious. The dialogue between archaeologists and architects has connected very old buildings to contemporary productions, around similar materials and techniques, simply facilitated by the tools available today. The extraordinary state of conservation of certain earthen architectures with elevations of several meters, after millennia of slow decay, proves the durability of this material, and its ability to respond to the principles of sustainability. Most of the solutions are in the past, it is for us to dig them up, revitalize them and adapt them to our contemporary needs, creating a connection between those who understand the past (archaeologists) to those who design the future (architects).

## Bibliography

* Amiet, P. (1988) *Suse : 6000 ans d'histoire*. Paris: Editions de la Réunion des musées nationaux.

* Daneels, A. and Guerrero Baca, L.F. (2015) ‘Archaeological earthen sites in America. Study and preservation’ in Gandreau, D. and Sadozaï, C. (eds) *Actes du séminaire international : la conservation des architectures de terre sur les sites archéologiques. Nouvelles pratiques et perspectives*. CRAterre-ENSAG, 26-28 mai 2014. Villefontaine : CRAterre, International scientific workshop 01: 92-103.

* Fontaine, L. and Anger, R. (2009) *Bâtir en terre. Du grain de sable à l'architecture*. Paris: Belin, Cité des sciences et de l'industrie.

* Gandreau, D. (2017) *Patrimoine archéologique en terre et développement local. Enjeux interdisciplinaires et perspectives de formation*. PhD Thesis. Grenoble: Université Grenoble Alpes, ENSAG.

* Gandreau, D. and Sadozaï, C. (dirs.) (2015) *Conservation des architectures de terre sur les sites archéologiques: nouvelles pratiques et perspectives*. Actes du séminaire international, ENSAG, 26-28 mai 2014 [online]. Available at: https://craterre.hypotheses.org/795 [accessed August 1 2020].

* Guillaud, H., Moriset, S., Sanchez Munoz, N., Sevillano Gutierrez, E. and Correia, M. et al. (2014) Versus: lessons from vernacular heritage to sustainable architecture [online]. CRAterre-ENSAG. Available at: https://hal.archives-ouvertes.fr/hal-01159770 [accessed: June 13 2019].

* Houben, H. and Guillaud, H. (1989) *Traité de construction en terre*. 3rd edn. Marseille: Parenthèses.

* Lecomte, O., Francfort, H.P., Boucharlat, R. and Mamedow, M. (2002) ‘Recherches archéologiques récentes à Ulug dépé (Turkménistan)’, *Paléorient*, 28(2): 123-132.

* Sadozaï, C. (2013) ‘Préservation de l’architecture de terre en Asie centrale : l’exemple du site protohistorique d’Ulug Dépé (Turkménistan)’ in *Bendezu-Sarmiento, J*. (dir.) *L’Archéologie*

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*française en Asie centrale. Nouvelles recherches et enjeux socioculturels*. Cahiers d'Asie Centrale n 21/22. Paris: Édition-Diffusion De Boccard: 623-630.

Sadozaï, C. and Gandreau, D. (2016) ‘Conserver après la fouille : la question des structures en terre crue à partir d’exemples en Asie centrale’ in Stucky, R.A., Kaelin, O. and Mathys, H.P. (eds) *Proceedings of the 9th International Congress on the Archaeology of the Ancient Near East: June 9-13 2014*, University of Basel. Basel: Harrassowitz, vol. 3: 781-789.

Sanchez Munoz, N., Moriset, S., Mecca, S., Dipasquale, L., Achenza, M., Mileto, C., Vegas Lopez-Manzanares, F., Correia, M. and Carlos, G. (2018) ‘Transmission de la méthode VerSus ‘from Vernacular to Sustainable’ aux étudiants et enseignants d’architecture: retour d’expérience’ in *Terra Education III*. Grenoble: CRAterre, AE&CC.

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