The site guarded a crossing-point of the River Ribble. The first known Roman activity was the building of a timber fort, believed to have been constructed during the campaigns of Petillius Cerialis around AD 72/3. This was replaced by a stone fort in the 2nd century. For most of its existence the fort was garrisoned by Sarmatianauxiliaries, first stationed in Britain by Marcus Aurelius in 175. Prior to that it is suggested that the fort was garrisoned by the Ala II Asturum from Spain, but there is some uncertainty about this. Pottery evidence indicates that the fort was occupied for most of the 4th century until the end of the Roman period.