Magnetic prospecting of the Roman military camp at Septimer Pass (Switzerland)

The Roman military encampment at the Septimer Pass (near Bivio, Switzerland) was located in 2003 using metal detectors. Dating between 15 BCE and 16 CE, the camp was designed for controlling the Pass, and to enable the movement of Roman troops between Italy and the northern province of Raetia. The 2-ha sized site was delineated by topography, aerial photographs, visible fortification walls and ditches, and the locations of finds. Subsequent trench excavations by the Bavarian Academy of Science were limited to 150 m2. Although these excavations provided a better understanding of the construction of the fortification walls, they gave no idea about the overall layout of tents or other buildings. For this study, magnetometry with a cesium-magnetometer in a duo-sensor configuration was used to survey an area of 160x120 m at a sampling interval of 25x50 cm. Some magnetic anomalies suggest geologic lineaments and modern cultural sources. Other anomalies support visual evidence of fortifications, suggest the outline of wooden barracks or contubernia used for military housing, and possibly the locations of watchtowers, pits and fireplaces. The magnetically clean zones between these anomalies correlate with the occurrence of tent nails that were found and cleared by the earlier metal detectorists, suggesting that these areas were primarily used for tents.