The island has over 240 bronze age burial mounds or round barrows, nearly all on the chalk downs. One plough-damaged barrow on Gallibury Down was excavated during 1979-80 and dated to between 1600-1400 BCE. There is also evidence from aerial photographs of ring ditches (the remains of barrows) on the limestone near Bembridge. The only significant Iron Age find is at Chillerton Down, where there was a hill fort. However three of the Roman villa sites have also produced late Iron Age pottery, which suggests a continuity of occupation.