When Antoninus Pius decided to venture beyond the wall built by his adopted father, Hadrian, and incorporate southern Scotland into the Roman Empire a second frontier wall was needed between the Forth and the Clyde to control the Northern tribes. Like Hadrian’s Wall the Antonine Wall made the best advantage of local geology and here at Croy Hill used a sill of hard volcanic dolerite. The name Croy comes from the Gaelic, cruaidh, meaning hard. But unlike Hadrian’s Wall the Antonine Wall was largely made of turf stacked like bricks to create a rampart 13 feet high and topped with a wooden palisade and a ditch on the outside. Forts were more frequent than on Hadrian’s Wall. There was one here at Croy Hill. It was constructed of stone which has been robbed leaving a few humps and bumps which hasn’t come up well in the photo.
The Antonine Wall was built in about 142 AD. It was abandoned in 160 AD and Hadrian’s Wall reoccupied. In the photo the centre of the fort is where the two trees are. The west gate where the boulder is. It would have stationed about a hundred men of the VI legion.