"One of the principal divisions of the parish of Llangollen, Nant Heudwy division of the hundred of Chirk, county of Denbigh; 2 miles (W) from Llangollen, containing 868 inhabitants. It forms the upper part of this picturesque parish, where the mountains are high and bold, while the river Dee winds at their feet in such an irregular course, as to make the landscape assume a fresh appearance of pleasing and diversified beauty at every turn." [A Topographical Dictionary of Wales, 1833 & 1849, Samuel Lewis]
The new parish of Pontfadog was formed on 15 April 1848, from the ancient parish of Llangollen. It comprised the whole of Glyn Traean - i.e. the townships of Cilcochwyn, Crogeniddon, Crogenwladus, Erwallo, Hafodgynfor, Nantygwryd, Pennant and Talygarth; and the township of Cysylltau from Llangollen Traean.
Cysylltau returned to Llangollen in 1870.