In A.D. 270 Roman army engineers constructed a major fort of more than 5 acres, with a masssive stone wall on all four sides, and enclosing or cutting through many earlier buildings.
The 8 foot-thick west wall of the fort (still standing to some 7 feet in height) cut through Rooms 3 and 4 of the Painted House.
The wall has been robbed in the southern part of the site, but a 16 foot length survives in the north area.
The wall was built from local materials, with the external face constructed from neatly squared blocks of calcareous tufa, and the inner face mostly of roughly squared chalk blocks. The foundation consisted of irregular masses of stone, brick and mortar -- mostly obtained from the demolition of the nearby buildings. The core of the wall was roughly constructed, containing much re-used material.