# Exploring Ephemeral Features with Ground-Penetrating Radar: An Approach to Roman Military Camps
###### Abstract  
This paper addresses an experimental approach to the archaeological study of Roman camps in NW beria using ground-penetrating radar (henceforth GPR). The main goal is to explore the capabilities of GPR to extract datasets from ephemeral features, such as temporary camps or siege works, among others. This information aims to maximise the data available before excavation, orienting it to areas that could provide good results in terms of feature detection and contrast between soil matrix and archaeological deposits. This paper explores the potential of the GPR approach and volumetric data visualisation to improve our understanding of four ephemeral sites: Alto da Raia (Montalegre, Portugal-Calvos de Randin, Spain), Sueros de Cepeda (Vilamejil, Spain), Los Andinales (Vilsandino, Spain), and Villa Maria (Sasamon, Spain). Despite the focus of this paper, other survey techniques (namely LiDAR, aerial photography, and magnetometry) were used in combination with GPR. Further excavation of the sites provided ground truthing for all data remotely gathered. ground-penetrating radar (GPR); remote sensing; roman army; Roman camps; Iberian Peninsula; volumetric visualisation +
Footnote †: journal: _remote sensing_  
conquest process is challenging for different reasons. Firstly, military field installations do not exactly stand out for their expressiveness in the archaeological record [11; 12]. Designed to be briefly occupied, their most distinctive features were defensive ramparts, parapets, palisades, ditches, and tents, of which very little remains today. In the absence of material culture (pottery, metallic objects, etc. ), the characterisation of these sites usually relies on identifying certain morphological elements, often considered canonical. Defensive perimeters in the form of a playing card (that is, a square or rectangle with rounded corners) or the presence of features such as _claviculae_ (prolongations of the ramparts forming a quarter of a circle) or _tituli_ (small, external traverse obstacles) guarding the gates are among the most recognisable elements. Secondly, we must consider the limitations derived from uneven dataset coverage in Spain and Portugal (especially concerning LiDAR data) and the geospatial product's spatial, spectral, and temporal resolutions. Since Roman military camps usually were huge enclosures now divided between several plots, we must further consider the moment of data capture in agricultural areas with different crops at different stages of the phenological cycle. Since vegetation's growth and degree of maturity significantly impact the visibility of the shallow underground archaeological remains, these factors limit the identification of the Roman military sites' defensive perimeter and the understanding of their internal distribution. Even if the growing availability of digital imagery from public and private sources fosters the recognition of previously unknown archaeological traces, only a few of these coverages are useful for archaeological purposes. This paper aims to tackle the study of the ephemeral traces of Roman temporary camps by applying a multi-modal approach in which remote sensing and geophysical survey are key. The overall aim is threefold: (1) to characterise archaeological features previously detected by other remote sensing methods; (2) to evaluate their preservation degree or physical characteristics through the interpretation of the geophysical data; and eventually, (3) to maximise the excavation results driven by GPR data. The application of the GPR survey in Roman temporary camps as proposed in this paper is innovative. In the Iberian Peninsula, most previous efforts have concentrated on studying permanent military structures [13] (Figure 1), chiefly using other techniques such as extensive magnetometry surveys. Figure 1: Location of the Roman camps studied in this paper within north-western Iberia. EPSG: 25830.