The Roman Map of Britain Gobannio or Gebannio Abergavenny, Monmouthshire

Bannio (R&C 53) next
Gobannio (AI 484₆ Iter xii)

Bannio is missing two letters when compared to AI's Gobannio. AI's form better matches the recorded river-name Geuenni ca.1150.

In a sequence along Margary 62 Isca Augusta.Burrio.Gebannio Caerleon-Usk-Abergavenny, the form Bannio could have been influenced by a preceding, but lost Burrio Usk. Further, it could be argued that Bannio is simply a wrongly copied Burrio. 

Abergavenny (SO3014)

A note of uncertain value 
In the Ravennas the -ge- of Branogenium is at a distance from the place before Bannio comparable to the length of the lacuna (skipped line) in the river section. A restored *Gebannio and *Branonium would more closely match the forms of AI recorded as Gobannio and Brauonio.