Caer Gai is a Roman auxiliary fort capable of housing a garrison in excess of 500 soldiers sited at a strategic point in the road system linking the forts at Chester, Caersws, Tomen y Mur and the fortlet at Brithdir. It was occupied from the conquest of the region in the 70s AD, through to at least the mid second century. The site is associated with the Cai Hir of Welsh literatrure and with Kay, the foster brother of Arthur. It was recognised as a Roman fortification in Camden's Britannia and in the mid sixteenth century a coin of Domitian was found. Edward Lluyd mentioned further features including a structure in 'Kae'r Kapele', which is probably a structure revealed by a recent geophysical survey in the annex on the south-eastern side of the fort. Modern archaeological investigation consists of limited excavation (Jarrett 1969; White 1986), air photo mapping and extensive geophysical surveys (Hopewell 2005 & Britannia 37 (2006)).

The fort is now a banked and ditched rectangular enclosure, about 130m north-east to south-west by 120m occupied by a sixteenth-seventeenth century mansion (NPRN 28254). The mansion's gardens filled the fort (NPRN 406900) and the visible walled circuit dates from this period. The fort wall, 1.35m wide can be seen crossing the farmyard.

The fort faced south-east across the meadows at the south-west end of Lake Bala. Ample traces of extramural settlement have been recorded on all four sides of the fort with annexes on the south-west and south-east sides, the latter containing a monumental building complex. Foundations of a small shrine associated with a scuptured stone block were noted on the west side and burials were recorded some 400m from the walls on this side. Some elements of a cropmark complex occupying a spur some 250m south of the fort (NPRN 406210) may be associated with the military settlement.

Sources: Thomas in Archaeologia Cambrensis 5th series II (1885), 196-205
Nash Williams in the Bulletin of the Board of Celtic Studies 8.4 (1950), 243-5
Bowen & Gresham 'Merioneth County History' I (1967), 235-7
Jarrett 'The Roman Frontier in Wales' 2nd edition (1969), 54-6
White in Archaeologia Cambrensis 135 (1986), 134-46
Hopewell in Britannia 36 (2005), 233-5, 260-5

John Wiles 07.06.07