There is more than one road in Wales bearing the Sarn Helen name, and the reason appears to be no more complicated than that Sarn Helen is Welsh for Road of the Legions, or Roman Road!
Sarn Helen East
This road is one of the better known of the Sarn Helen routes, although the tag of east is a little misleading as it meanders across the hills of northern Carmarthenshire and over the border into Cardiganshire.
A little to the north is another Sarn Helen, which may or may not be part of the same road. It can be found in the vicinity of Strata Florida Abbey (if memory serves correctly).