The caves of the Mendip Hills were settled during the Neolithic period and contain extensive archaeological sites such as those at Cheddar Gorge. There are numerous Iron Age Hill Forts, which were later reused in the Dark Ages, such as Cadbury Castle, Worlebury Camp and Ham Hill. The age of the henge monument at Stanton Drew stone circles is unknown, but is believed to be from the Neolithic period. There is evidence of mining on the Mendip Hills back into the late Bronze Age when there were technological changes in metal working indicated by the use of lead. There are numerous hill forts, such as Small Down Knoll, Solsbury Hill, Dolebury Warren and Burledge Hill, which seem to have had domestic purposes, not just a defensive role. They generally seem to have been occupied intermittently from the Bronze Age onward, some, such as Cadbury Camp at South Cadbury, being refurbished during different eras. Battlegore Burial Chamber is a Bronze Age burial chamber at Williton which is composed of three round barrows and possibly a long, chambered barrow.