One of three pill boxes built to defend the Garreg-ddu dam (nprn 752) and Foel Valve Tower (nprn 32527). It is a variant of the standard War Office design FW3/22, hexagonal in shape, measuring 4.65 metres in length, 4.16 metres in width and 2 metres in height. Built of reinforced concrete with inner and outer red clay brick shuttering. Exterior anti-blast wall, made of bricks to cover entrance.
Source: Cadw scheduling description.
F.Foster, RCAHMW, 17.10.2008.