Knucklas was constituted a borough in 1246. Settlement here was limited and focused on the important castle which was constructed by the Mortimer family in the 1240s (nprn: 306398). The castle was captured by the Welsh in 1262 and both it and the settlement fell into decline. It is possible that a few burgesses remained during the later middle ages (Soulsby, pp. 156?7).

A 13-arch span Victorian viaduct (nprn: 43058) was completed in 1865 on the section of the Central Wales Railway running through Knucklas.

References:
Soulsby, I; The Towns of Medieval Wales, 1983.
NMR site files.