This is the largest monument of its kind in Britain, and possibly in the world.
It dates from some 4,000 years ago during the late New Stone Age period.
The circle consists of a roughly circular bank, now about 5 metres high but once much larger, enclosing an area of over 11 hectares. The bank is cut by a ditch and originally, on the inner edge of the ditch, there stood almost 100 great sarsen stones, each of which may have weighed as much as 50 tons with half of each stone being buried in the earth. Sarsen stones which litter many parts of the downs are the remains of a sandstone layer laid down on top of the chalk. The softer parts were worn away by the ice leaving these large boulders in the landscape. Sarsen stones are extremely hard and are said to have derived their name from the Saracens, an alien people.
The enclosure is cut into four quarters by entrances and there are two more circles within the main enclosure. It's generally accepted that the Stone Circle represented a social and/or religious centre for the primitive farming communities in the Wessex downland.
The Stone Circle and surrounding land is managed by the National Trust and can be visited at any time.
This Iron Age hill fort commands the head of the valley of the River Og which provided one of the main approaches into Wessex from the north. From here you can see Liddington Castle, the second hill fort encountered in this section, on the opposite side of the valley to the northeast performing the same role.
At Barbury the Battle of Beranburgh took place in 556 as the Saxons from the Upper Thames Valley pushed south into Wiltshire conquering the Romano-British.
The hill fort covers over 4 hectares and has double ramparts, a ditch and two entrances. Excavations of the site have shown evidence which suggests Barbury Castle was continuously occupied through the Roman period to Saxon times.
The Castle and country park around it are managed by Swindon Borough Council. There is ample parking, and toilets.
Hill forts which The Ridgeway passes west of the Thames are: Barbury Castle, Liddington Castle, Uffington Castle, and Segsbury Camp. East of the Thames they are: Pulpit Hill and Ivinghoe Beacon.