A relatively small circle of 20-foot-tall rocks on the British Isles, Stonehenge has intrigued men throughout the ages. In the 12th century, Geoffrey of Monmouth claimed that a tribe of giants brought Stonehenge from Africa to Ireland, where the wizard Merlin moved it to its present location. Later theories suggested that its early uses might have been as a temple of Druidic worship and human sacrifice. In the 20th century, astrologers have postulated that it served as a complex astrological observatory, computational device, and calendar system which contributed to a better system of planting and harvesting.