This was a five-hundred strong infantry unit recruited from the Baetasii tribe inhabiting the lands between the Rhine and the Meuse to the immediate west of Novaesium in Germania Inferior (Neuss, Westfalen, West Germany). It is possible that they formed the first century garrison at Manchester, and were moved to Old Kilpatrick at the western end of the Antonine Wall around 139AD. A detachment of the unit apparently manned the small fort at Bar Hill in the central portion of the Wall during the Antonine period, and this may have been due to prior experience in the area gained during the Agricolan campaigns through Scotland. It is possible that a detachment of this unit were posted to assist the main Antonine garrison, Cohors I Hamiorum Saggitariorum, a unit of archers from Syria. Coh I Baetasiorum were moved to Maryport during the late Antonine period, where the experience gained in the maritime environment on the Cumbrian coast was later to see the unit posted to the Saxon-Shore fort at Reculver in Kent.
Evidence for the presence of Cohors Primae Baetasiorum civium Romanorum in Britain
- Burn 95; CIL XVI.48; military diploma, dated: January 19th 103AD.
- Burn 100; CIL XVI.65; military diploma dated: July 17th 122AD.
- Cil Vii.1195; privilegia militvm, dated: September 16th 124AD.
- Manchester (RIB 581).
- Old Kilpatrick (RIB 2213b, altar?).
- Bar Hill (RIB 2169, altar; 2170, 139-161AD).
- Maryport (RIB 830; 837/838; 842/843; all altars).
- Reculver (Notitia Dignitatum).