There are intermittent traces of a roughly 650m stretch of Roman road passing through Blaengwrthyd on Mynydd Illtud. The road runs rather south of north-east from the given grid reference for some 625m, before bearing to the north. It is last seen at SN97532712. This is part of the route between Coelbren & Brecon Gaer (RR622: NPRN 407122).

A distinct agger, or causeway, is visible at the western end of this section. It is generally 7.8m wide and 0.25m high, with a level surface 3.3m wide. Where it runs to the north a roughly 5.0m wide terrace can be seen. This section marks the end of a 4.0km alignment. The next sections lie either side of the crossing of the Nant-y-llest (NPRN 275631) some 850m to the south-west.

Sources: Jones in Archaeologia Cambrensis 106 (1957), 58
RCAHMW Brecknock Inventory: Prehistoric & Roman (1986), 162

T. Driver, RCAHMW, 2015