Blaenavon Ironworks began production in 1789 with 3 furnaces. Two more furnaces were built c1810. The original partnership, led by the Hill family, sold the works in 1836 to the Blaenavon Iron and Coal Co. Initial investment at the site included the construction of a water balance lift for conveyance of pig iron from the site, but further investment did not occur until the 1850s. A new blast engine was built, and a new furnace was blown in during 1861. Investment was also made on a new site kown as Forgeside. By 1900 only one furnace remained in blast, but this was blown out in 1904. Thereafter the site was used by small-scale engineering companies until it became a guardianship monument in 1974.

Furnaces 4 and 5 were built c1810 and the cast house was contemporary with them. It was demolished in the late C19.
Rubble-stone walls of a former cast house, up to 1.5m high. The cast house, originally approximately 20m square, retains part of its S wall, with splayed angle to the R (E) end and a wide opening infilled with brick. It is cut by later tramways (nprn 67629, 67632) in the side walls. The interior is a raised platform.

R Hayman, Hayman & Horton, 6/1/2003