Situated on a stark, bare hill in the Preseli Mountains is Foel Drygarn Hillfort. It has two rings of stonework crowning its top, and two great banks to discourage intruders. Inside are 220 hut circles, in which lived a large Celtic population from about 300 BC. The three burial mounds on the very top initially appear to be heaps of random stones, but a close inspection reveals carefully constructed cairns within which are circular depressions. The Preseli Mountains are steeped in ancient history and are the area from which [almost incredibly] the bluestone rocks used at Stonehenge were taken.