# Exploring Ephemeral Features with Ground-Penetrating Radar: An Approach to Roman Military Camps
## 2 Materials and Methods
### Case Studies
#### 2.2.1 Alto da Raia (Calvos de Randin, Ourense, Spain-Montalegre, Vila Real, Portugal)  
The Alto da Raia camp (Figure 4(1a,1b)) shows an overall rectangular layout with rounded corners and straight lines connecting them. It was recently discovered thanks to the processing and analysis of the LiDAR data provided by the Spanish IGN-PNOA project. The data made it possible to document a fortified enclosure of approximately 3 ha in size, built on a hill at circa 883 m asl overlooking the valley of the Salas River. The camp of Alto da Raia is located on a Palaeozoic granite and rocky slate zone, with optimal conditions for the GPR survey regarding soil conductivity and even terrain for the equipment configuration (Figure 6). The SPLAL aerial imagery (1949) acquired from the Geospatial Information Centre of the Portuguese Army (CIGeoE) shows that the camp's location has not been subject to agricultural practices, except for a few areas nearby that no longer serve this purpose.  
The archaeological survey--using LiDAR, UAV-derived photogrammetry (see hill-shade visualisation in Figure 7), geophysics (magnetometry and GPR), and excavation--carried out in 2021 validated its characterisation as a Roman military camp. Publication of the results is underway. Although quite flattened on its southern side, an earther ramp  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Camp**} & \multirow{2}{*}{**Location**} & \multicolumn{2}{c}{**UTM**} & \multirow{2}{*}{**Camp Size**} & \multirow{2}{*}{**Documented Features**} & \multirow{2}{*}{**Area of Interest**} & \multirow{2}{*}{**Grid Size (m)**} & \multirow{2}{*}{**Survey Area** (sq. m)**} \\  & & **Cerdinate** & & & & & \\  & & **(X; Y)** & & & & & \\ \hline \multirow{3}{*}{Alto da Raia} & \multirow{3}{*}{Montalegre, PT} & 94,286; & \multirow{3}{*}{3.02} & \multirow{3}{*}{\begin{tabular}{c} Irregular \\ playing-card \\ layout (earthwork and \\ trench) \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} Possible gate \\ 60 \(\times\) 15 \\ \end{tabular} } & \multirow{3}{*}{60 \(\times\) 15} & \multirow{3}{*}{900} \\  & & & & & \\ \cline{1-1}  & & & & & \\ \cline{1-1}  & & 249,862; & \multirow{3}{*}{13.49} & \multirow{3}{*}{\begin{tabular}{c} Playing-card \\ layout (trench) \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} Camp defences \\ 10 \(\times\) 40 \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} 100 \(\times\) 40 \\ \end{tabular} } & \multirow{3}{*}{400} \\  & & 412,411; & & & \\ \cline{1-1}  & & 4,694,680 & & & & \\ \cline{1-1}  & & 412,411; & & & & \\ \cline{1-1}  & & 4,694,680 & & & & \\ \cline{1-1}  & & 4,694,680 & & & & \\ \cline{1-1}  & & & & & & \\ \cline{1-1}  & & 412,053; & \multirow{3}{*}{2.5} & \multirow{3}{*}{\begin{tabular}{c} Sieg structures \\ and possible \\ playing-card \\ clamp (trench) \\ \end{tabular} } & \multirow{3}{*}{\
\begin{tabular}{c} Sieg structures- \\ Camp \\ defences \\ \end{tabular} } & \multirow{3}{*}{
\begin{tabular}{c} 15 \(\times\) 20 \\ \end{tabular} } & \multirow{3}{*}{300} \\ \cline{1-1}  & & 412,053; & & & & \\ \cline{1-1}  & & 4,693,011 & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Roman camp locations, morphology, and extent of the survey areas analysed in this paper.  
was documented delimiting the site, whereas an external V-shaped ditch complemented the defences. The GPR survey aimed at identifying the eastern entrance to the camp, a feature relevant to deepen the characterisation of the site and to understand its internal structure.