The prehistoric monument underwent several modifications beginning more than 5,000 years ago and did not begin as a circle of stones. It started out as a modest earthwork enclosure where prehistoric humans buried their dead. The circular earth bank and ditch that surrounds the stones date back to roughly 3,100 BC, while the monument's inner stone circle was built in the late Neolithic period, circa 2,500 BC. The stones were rearranged and new ones were placed during the next few hundred years, with the formation as we know it today being completed between 1,930 and 1,600 BC.