City of the Legions
Latin: Isca Legionis, Urbs Legionis
Geoffrey refers to it several times, but means it to be Caerleon-on-Usk, which was called Isca Legionis and Isca Legionum in early times. K.H. Jackson identifies it unhesitatingly as Chester, known by the Romans as Urbs Legionis in Latin. Another possibility of Castleford, which was known as Legiolium in Roman times.
The city of York (Eboracum) holds the epithet of “City of the Legion” due to the presence of the Ninth Legion.
Isca Legionis is a Latin term, which translates to “Legionary Fort” or “Legionary Camp.” Isca Legionis is specifically associated with the town of Caerleon in Wales. Caerleon was known as Isca Augusta during Roman times and it served as the base for the Second Augustan Legion (Legio II Augusta). It is an alternative name for the same Roman settlement.
Urbs Legionis is a Latin term that translates to “City of the Legion.” It could be used to describe any Roman settlement that functioned as a legionary fortress. The term does not refer to a specific location but rather highlights the military significance of the settlement as a legionary base.
Historia Brittonum | Probably Nennius, early 9th century