The fort was replaced by a fortlet, also built using turf and timber, in AD 105. Although the fortlet was built on the same site as the fort, it did not use the same foundation trenches. There were two construction phases of the fortlet, the second – dating to c. 120 – featured gates, an oven, a well, a granary, a hypocaust a workshop, barracks, a commanders house, a courtyard building, and possibly a latrine. The barracks were built to accommodate 48 soldiers and even with administrative staff and officers, the garrison of the fortlet would have numbered less than 100. The first phase was laid out along the same lines as the second phase. The fortlet defences – as with most other fortlets – were designed to withstand attacks from brigands or hold off an enemy until reinforcements from the main army could arrive rather than withstand a determined attack. A civilian settlement or "vicus" grew around the fortlet in the early 2nd century. It probably would have been home to those who benefited from trade with the garrison or hangers on of the soldiers. Since it is unlikely that a garrison of under 100 could have supported a "vicus", it has been suggested that the fortlet was a commissary fortlet, one which was the administrative and logistical centre of part of the Roman army. With soldiers regularly arriving to collect pay and orders, a "vicus" could have been supported. The fortlet fell out of use in the mid 120s. The fort and fortlet of Castleshaw were superseded by the neighbouring forts at Manchester and Slack. The "vicus" was abandoned around the same time as the fortlet fell out of use.