City of the Legions
Latin: Isca Legionis, Urbs Legionis
A city in Britain that was the scene of Arthur’s ninth battle against the Saxons, according to Nennius. As in all of the twelve battles, Arthur was victorious.
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.
Urbs Legionis is a Latin term that translates to “City of the Legion.” In the context of Roman Britain, Urbs Legionis is often associated with the Roman town of Caerleon, which is located in modern-day Wales. Caerleon was known as Isca Augusta during Roman times. Caerleon served as the base of operation for the Second Augustan Legion (Legio II Augusta).
Isca Legionis is another Latin term, which translates to “Legionary Fort” or “Legionary Camp.” Isca Legionis is specifically associated with the town of Caerleon, as mentioned above. It is an alternative name for the same Roman settlement.
See also
Isca Legionis | The Legend of King Arthur
Source
Historia Brittonum | Probably Nennius, early 9th century