West Kennet Longbarrow is a Neolithic tomb or barrow, near Silbury Hill, close to Avebury in Wiltshire. It is one of the many prehistoric monuments that are part of the Avebury complex of Neolithic sites.

The long barrow stretches for 100 metres in an East - West orientation. The earth used in its construction was taken from two trenches dug alongside the mound, although these have long since become filled with weathered material. The chamber, which extends 10 metres into the mound, consists of five separate small chambers, two on either side of a narrow passage, which then opens up into a further chamber at the far end. Like many of these passage graves, the entrance was flanked by a semi circular forecourt, which framed the dark opening, although this is now partially obscured by the huge stones used to seal the tomb. These large stones, and the other hefty sarcen stones that were used in the barrows construction, were brought from the nearby downs, while the smaller stones were brought from a location over 30 miles away. The tomb is thought to have been constructed around 3500BC, and was in use for a thousand years, until 2200BC, when the tomb was sealed with chalk rubble, and the gigantic sarcen boulders that now guard the entrance. This was at the same time as the great stone circle at Avebury was begun, and may signify a change in the focus of belief and religion.

West Kennet Longbarrow is thought to have been constructed around 3500BC, and was in use for a thousand years, until about 2200BC, when the tomb was sealed with chalk rubble, and the gigantic sarcen stones that now guard the entrance. The passage and chamber were filled to the roof by the Beaker people with earth and stones, among which were found pieces of Grooved ware, Peterborough ware and Beaker pottery, charcoal, bone tools, and beads. This was at the same time as the great stone circle at Avebury was begun, and may signify a change in the focus of belief and religion.

The long barrow has been damaged by indiscriminate digging, but archaeological excavations in 1859 and 1955-56 it was revealed that almost 50 people - of varied age groups, from babies to elderly persons, were buried within the tomb. These people may have been the ruling elite from the farming community that made the Avebury area its home. Evidence also suggests that the leg bones and skulls were removed for use elsewhere, although the ceremonies, and the meaning of them will probably never be fully understood. It has been suggested that the bodies were first laid out to rot in a separate place, perhaps the sanctuary at nearby Overton, or as part of the complex rituals that took place at Windmill Hill.

The latest excavations also revealed that the side chambers occur inside an exact isosceles triangle, whose height is twice the length of its base. Artifacts associated with the burials include Neolithic Grooved ware similar to that found at nearby Windmill Hill.