here. Buried under a Serbian cornfield close to a coalmine, the well-preserved remains of a Roman legion's headquarters are being excavated by archaeologists who say its rural location makes it unique. Covering an estimated 3,500 square meters, the headquarters - or principium - belonged to the VII Claudia Legion. Its location was deduced in the spring during a survey. The compound, which lies east of Belgrade and around one meter (3 ft) under the surface, had 40 rooms with heated walls, a treasury, a shrine, parade grounds and a fountain. So far only a quarter has been explored, with excavations scheduled to resume next spring. Inside one room, archaeologists found 120 silver coins that "must have been lost during an emergency" such as an invasion or a natural disaster, said the principium's lead archaeologist Nemanja Mrdjic. "The distribution of coins from a corner to the door, ... suggests they (coins) spilled while someone was fleeing." The VII Claudia Legion was active between 2nd and 5th centuries AD, and its walled camp and principium were separated from the rest of Viminacium, which had its own fortifications.