The Bwlch y Groes (Pass of the Cross) and its side road Bwlch Eunant probably have a history as a road that lies back in the dark days long before things were ever thought of being recorded as existing. The road summit at 545m, (1788ft) is often claimed to be the highest public road in Wales, however, as far as surfaced roads go, that honour is held by the Bwlch yr Efengyl (Gospel Pass) 549m, (1801ft) in the Black Mountains of South East Wales also used by the ISDT in Wales although its approach is not as steep as the Bwlch y Groes. The unsurfaced Bwlch Llandrillo in the Berwyns, also used in the ISDT, crosses the 580m 2000ft contour at the summit of the pass. The ISDT, when on the Bwlch y Groes, never crossed the high summit as detoured to travel to Bala via the gnarly old tracks through the Euanant and Hirnant valleys. History paints a picture of the route being in use by religious travellers passing between the early Celtic Christian sites and the many Monasteries, Abbeys, Friaries and Priories the church of Rome had established at Welshpool, Llangollen, Llanrwst, Holywell, Flint, Denbigh, Llaneltyd before the reformation. But it was mostly motorsport rather than tourism that rediscovered the opportunities the then many unsurfaced road provided in the early development of motoring on public roads.
C Smiths map of England and Wales 1806 clearly shows the route of the Bwlch y Groes and the Bwlch Eunant long before the construction of the Reservoir on the Vyrnwy by the Liverpool Corporation.