A Roman supply base that was part of a complex.
History
Excavations near the Cae Hywel orchard has unearthed remains of a Roman fort, including a barracks for legionaries, linked to a centurion's house. The fort is shaped like a pentagon and stands near the Afon Vyrnwy. It was only discovered by aerial survey in 1986 and excavated shortly after. The ramparts surrounding the fort are 5 metres wide, with 2 ditches. The inner ditch is almost 7 feet wie while the outer ditch is 10 feet across. Each ditch is approximately 3.5 feet deep. Together the ditches enclose an area of around 2.75 acres.

Within the fort investigation found indications of a timber granary and post holes supported a barrack roof. Inside the fort perimeter was a metalled track, or patrol road. A public footpath runs across the north slope of the hilltop site, allowing access from Llansantffraid-ym-Mechain village centre.

The Romans may also have been responsible for earthworks at Plas-Yn-Dinas, 1 mile to the south, where excavations revealed a rectangular site, roughly 80 metres by 100 metres, defended by two ditches, possibly suggesting 2 distinct phases of occupation. The original conclusion based on the excavations was that the site represented a supply depot for the Roman army.

However, some historians dispute this, as no Roman objects wee unearthed. So, is the second site at Llansantffraid-ym-Mechain a Roman remain, or is it a late prehistoric enclosure surrounding a small settlement? The evidence seems inconclusive, and as it stands now there is very little to see on the ground.