The site of the Roman auxiliary fort is represented by a platform roughly 100m square and whose bank and ditch survive on the south-west side, running parallel with the modern road. The next field to the south-east corresponds to a walled annex containing a bathhouse and other buildings. The fort was excavated from 1899 (Ward 1903, 1909, 1911, 1913) and the findings were later reconsidered (Simpson 1963, 49-66; Black 1993).

An auxiliary fort such as this held a garrison of about 500, divided between six centuries of eighty soldiers, accommodated in six barrack blocks. The fort was at the centre of an extensive settlement (see NPRN 275863). It is suggested that the first fort on this site was of timber construction, probably later first century AD, itself a successor to the larger fort enclosure to the north (NPRN 300144). From about 100 AD the fort walls and buildings were rebuilt in stone or upon stone footings. It is thought that the fort was garrisoned throughout the second century and that some form of occupation, possibly official rather than military, continued up to the end of the Roman period.

Sources: Ward 'The Roman Fort at Gelli Gaer' (1903)
in the Transactions of the Cardiff Naturalists Society S42 (1909), 25-69
S44 (1911), 65-91
S46 (1913), 1-20
Simpson in Archaeologia Cambrensis 112 (1963), 13-76
Jarrett 'The Roman Frontier in Wales' 2nd edition (1969), 88-91
RCAHMW 1976 Glamorgan Inventory 1.2 (1976), 95-8 No. 737
Black in Britannia 24 (1993), 249-54

John Wiles, RCAHMW, 16 October 2007