“They heard of the Great Barrows, and the green mounds, and the stone-rings upon the hills and in the hollows among the hills. Sheep were bleating in flocks. Green walls and white walls rose. There were fortresses on the heights.” 
As well as the barrows and stone-circles of my two previous posts, the Wessex Downs have quite a large number of Iron Age fortresses on the hilltops. The closest of these to Avebury, and the first I visited was Barbury Castle, a few miles south of Swindon.
Barbury Castle is perhaps the most remarkable of the Ridgeway hill forts. It’s on the edge of the Marlborough Downs with views in all directions, on the Ridgeway, and it’s huge! It is defined by a broadly elliptical double rampart with a ditch in between, which even after two millennia of erosion, remains quite steep and imposing. The fort was built in the 6th century BC as a refuge against warring tribes. At times of attack, people would bring their animals and shelter in huts inside the 12 acre enclosure. The outer bank was reinforced by huge sarsen stones and the inner bank was topped by chalk blocks and a continuous wooden fence.
The fortress is clearly visible in this satellite photo, taken from Google Earth Pro, and also just outside the western entrance can be seen a round barrow which dates from 1,700 BC.