Avebury is the site of a large henge and several stone circles in the English county of Wiltshire surrounding the village of Avebury. It is one of the finest and largest Neolithic monuments in Europe dating to around 5,000 years ago. It is older than the megalithic stages of Stonehenge, which is located about 32 kilometers (20 mi) to the south, although the two monuments are broadly contemporary overall. It lies approximately midway between the towns of Marlborough and Calne, just off the main A4 road on the northbound A4361 towards Wroughton. The henge is a Scheduled Ancient Monument and a World Heritage Site. Avebury is a National Trust property.

The Monument
Most of the surviving structure consists of earthworks known as the dykes, consisting of a massive ditch and external bank henge 421 meters (1,381 ft) in diameter and 1.35 kilometers (0.84 mi) in circumference. The only known comparable sites of similar date (Stonehenge and Flagstones in Dorset) are only a quarter of the size of Avebury. The ditch alone was 21 meters (69 ft) wide and 11 meters (36 ft) deep, with its primary fill carbon dated to between 3400 and 2625 BC. A later date in this period is more likely although excavation of the bank has demonstrated that it has been enlarged, presumably using material excavated from the ditch. The fill at the bottom of the final ditch would therefore post-date any in an earlier, shallower ditch that no longer exists.

Within the henge is a great Outer Circle constituting prehistory’s largest stone circle with a diameter of 335 meters (1,099 ft). It was 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. They varied in height from 3.6 to 4.2 m as exemplified at the north and south entrances. Carbon dates from the fills of the stone holes date between 2800 and 2400 BC.

Nearer the middle of the monument are two other, separate stone circles. The Northern inner ring measures 98 meters (322 ft) in diameter, although only two of its standing stones remain with two further, fallen ones. A cove of three stones stood in the middle, its entrance pointing northeast.

The Southern inner ring was 108 metres (354 ft) in diameter before its destruction. 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 until their destruction in the eighteenth century. There is an avenue of paired stones, the West Kennet Avenue, leading from the south eastern entrance of the henge and traces of a second, the Beckhampton Avenue lead out from the western one.

Aubrey Burl conjectures a sequence of construction beginning with the North and South Circles erected around 2800 BC, followed by the Outer Circle and henge around two hundred years later and the two avenues added around 2400 BC.

A timber circle of two concentric rings, identified through archaeological geophysics possibly stood in the northeast sector of the outer circle, although this awaits testing by excavation. A ploughed barrow is also visible from the air in the northwestern quadrant.

The henge had four entrances, two opposing ones on a north by northwest and south by southeast line, and two on an east by northeast and west by southwest line.