Taff Vale Railway Viaduct over Mill Street including masonry weir

The Taff Vale Railway Viaduct over Mill Street, which includes a masonry weir, is a significant structure built in coursed rock-faced stone in two phases. The earlier phase, located on the eastern side of the bridge, is wider and features a single elliptical skewed arch that spans the river, along with two round-headed arches on the southern bank. The northernmost arch has an arched watercourse beneath it, while the southernmost is integrated into the bank. Thick bands are present at the impost level and below the parapet, which has been rebuilt.

The later phase is also single-track and consists of two segmental arches that span the river. The central pier features rounded cutwaters, and the northernmost bay is now occupied by Mill Street, which is carried over the river on steel piers. A third, narrower arch on the southern bank crosses a bypass channel from a weir located beneath the main arches. The parapet in this section has also been rebuilt and includes a projecting band over the right-hand side of the main arches only. The abutment on the northern side is a later addition, constructed to support a plate girder bridge over Rhondda Road.

Additionally, a weir is built across the two later river arches, consisting of a dam made of coursed stone that is approximately 1.2 meters high, with stone paving on the downstream side. An arched sluice projects from the northern end, while the main bypass channel is situated on the southern side.