Excavations in and around the castle over the years have found Palaeolithic flint implements, Neolithic stones and pottery and Roman coins. Traces of Iron Age ramparts have also been identified.
In May 2010 Time Team carried out a three day dig on Castle Green. In one trench (Trench 1 just outside the north wall of the castle) flint and prehistoric pottery was found. Of the 33 pieces of worked flint one was a chisel arrowhead of late neolithic date. The same trench also produced 35 pieces of pottery broadly dated to the Iron Age. The results suggest the possible remnants of an Iron Age rampart in the area.