The term British Prehistoric Monument refers to Stonehenge, a prehistoric monument located in Wiltshire, England. It is believed to have been constructed between 3000 and 2000 BC and is composed of a ring of standing stones, each around 13 feet high, 6 feet wide and weighing around 25 tons. The purpose of the monument is still unknown, but it is thought to have been used for religious or ceremonial purposes.