It is dramatically positioned on the end of the mile-long crag of the Whin Sill over which the Wall runs, overlooking sparsely populated hills.

A major rebuilding in the late 3rd/early 4th century included interval towers on the walls, a huge horreum (warehouse) and new barracks.

A substantial civil settlement (vicus) existed to the south, outside the fort, and some of the stone foundations can still be seen, including the so-called "Murder House", where two skeletons were found beneath an apparently newly-laid floor when excavated.

It is unusual for Britain in that it had no running water supply and was dependent upon rainwater collection for which purpose there is a series of large stone-lined cisterns around the periphery of the defences).

In the 2nd century AD, the garrison consisted of an unknown double-sized auxiliary infantry cohort and a detachment of legionaries from Legio II Augusta.