Garnddyrys Forge was built in 1816 -17 by Thomas Hill II, in conjunction with a tramroad from the furnaces at Blaenavon to the Brecon & Abergavenny Canal at Llanfoist. In 1817 the market for iron was extremely depressed and so investment in a new forge at that time is surprising. The site had a population of approximately 450 in the 1840s. After the railway reached Blaenavon in 1854 Garnddyrys was in an isolated position, and a new forge (known as Forgeside) was in due course built at Blaenavon closer to the railway.

Garnddyrys Forge probably ceased working circa 1861 when the tramroad was given up. Its relatively short period of operation, and the fact that the site has not been redeveloped, makes the site of national importance as an archaeologically well-preserved early nineteenth century forge.

The remains of this extensive site include two reservoirs (NPRNs 91628 & 91630), sites of waterwheels, puddling furnaces (NPRN 91627) and workers' housing (NPRN 91618). Hill's Tramroad (NPRN 85860) passed through the site in a tunnel and was used to bring cast iron from Blaenavon Ironworks (NPRN 34134) and convey wrought iron from the forges to the Brecknock & Abergavenny Canal (NPRN 85124) at Llanfoist Wharf (NPRN 34553). The foundations of the workers houses were excavated in 1970.

RCAHMW, 14 July 2011.

Sources:
R Hayman, Hayman & Horton, 26/11/2003
A Guide to the Industrial Archaeology of South East Wales, AIA, 2003