The fort was rebuilt four times, and each time was raised up by adding fill. Periods I-II date from AD 47-69; periods III-IV date from 70 to the end of the 2nd century; and period V dates from the end of the 2nd century to the middle of the 3rd century. The fort was made of wood in periods I-IV, in size, with ramparts made of earth and wood. In period V it was rebuilt of stone and increased in size to . At this time the gates were flanked by stone
gate towers with semi-circular
bastions on the exterior. The fort contained the headquarters building, or
principia, within a rectangular courtyard surrounded by a colonnade (
portico). The building had
hypocaust underfloor heating. Throughout the fort's existence the
principia was about with an atrium, cross hall and five rooms. The central room was the shrine of the legions' standards, or
sacellum. This room and the atrium both held stone altars in period V. A protective
ditch surrounded the fort throughout its Roman occupation. There were
vici to the east and west of the castellum where craftsmen lived who depended on the soldiers. The eastern
vicus was at , on the river bank. ==Excavations==