The earlier bridge had been criticised as not even wide enough for a horse and cart, therefore the new bridge was wide enough for a double carriageway. A single arch spanned 143 ft (43m) across the river, rising 35 ft (10.5m) above it (at the time it was the third longest single arch in Britain). The height of the bridge essentially reduced the gradient of the road towards the town. The bridge, arch soffits, parapets and buttresses are faced with chisel- or hammer-dressed masonry, while the voussoirs of the arch are lengthy and finished with ashlar. Large stone buttresses marked each end of the arch, and similar buttresses continued in either direction from the bridge supporting the long causeways towards Llandeilo and Ffairfach.
