In the original plan for Hadrian?s Wall (begun in AD 122) there were no forts on the Wall itself. Within two years, however, the decision was taken to add 15 forts to the line, to be manned by units of auxiliary troops (those who were not citizens of Rome). The earliest of the new forts straddled the Wall, lying half to its north and half to its south. This was the case at Chesters, where the ditch that fronted the Wall was filled in and a recently built Wall turret demolished to make way for the fort.
A Hadrianic inscription shows that the unit stationed in the new fort was the 500-strong ala Augusta ob virtutem appellata ? ?the cavalry regiment styled Augusta for its valour?. This cavalry unit would have required 16 stable-barracks, each housing some 32 men and their mounts.