Outer Stone Circle
Within the henge is a great outer circle. This is one of Europe's largest stone circles, with a diameter of 331.6 metres (1,088 ft), 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 in excess of 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 BCE (3870+/-90, 4130+/-90).
The two large stones at the Southern Entrance had an unusually smooth surface, likely due to having stone axes polished on them.
Inner Stone Circles
Nearer the middle of the monument are two additional, separate stone circles. The northern inner ring is 98 metres (322 ft) in diameter, but only two of its four standing stones remain upright. A cove of three stones stood in the middle, its entrance facing northeast. Taking experiments undertaken at the megalithic Ring of Brodgar in Orkney as a basis, the archaeologists Joshua Pollard, Mark Gillings and Aaron Watson believed that any sounds produced inside Avebury's Inner Circles would have created an echo as sound waves ricocheted off the standing stones.
The southern inner ring was 108 metres (354 ft) in diameter before its destruction in the 18th century. The remaining sections of its arc now lie beneath the village buildings. A single large monolith, 5.5 metres (18 ft) high, stood in the centre along with an alignment of smaller stones.