Within the henge is a great outer circle. This is one of Europe's largest stone circles, with a diameter of , Britain's largest stone circle. It was either contemporary with, or built around four or five centuries after the earthworks. There were originally 98 sarsen standing stones, some weighing over 40 tons. The stones varied in height from 3.6 to 4.2 m, as exemplified at the north and south entrances. The fill from two of the stoneholes has been carbon dated to between 2900 and 2600 BC (3870+/-90, 4130+/-90)