The route then leads on past Llan Ffestiniog to the Roman fort of Tomen y Mur, near Trawsfynydd before continuing south towards Dolgellau.

[4] Sarn Helen might have crossed the Afon Dyfi at a ford or ferry near Cefn Caer, a small Roman fort at Pennal in southern Gwynedd.

The route then heads southeast towards the Dolaucothi Gold Mines near Pumsaint, Carmarthenshire, before passing the substantial Roman fort of Luentinum before finally reaching its historical end at Alabum (modern-day Llandovery).

A further section of Roman road leading north-eastwards from Neath (Nidum) to Banwen at the southern edge of the Brecon Beacons National Park is also known as Sarn Helen.

It continues north-eastwards through the park to the north-west of Ystradfellte, beneath Fan Frynych, and then across Mynydd Illtud en route to the Roman fort of y Gaer (Cicucium).

It is also the title of a 1997 sequence of poems by English poet John Wilkinson and a 2023 travel book by Tom Bullough, who walked the route in 2020.