Monnow Bridge, located in the town of Monmouth, is the only remaining fortified river bridge in Great Britain with its gate tower standing on the bridge. Such bridge towers were common across Europe from medieval times, but many were destroyed due to urban expansion, diminishing defensive requirements and the increasing demands of traffic and trade. The historical and architectural importance of the bridge and its rarity are reflected in its status as a Scheduled Monument and a Grade I listed building. The bridge crosses the River Monnow (Afon Mynwy) 500 metres (1,600 ft) above its confluence with the River Wye.
Built predominantly of Old Red Sandstone, the bridge was the subject of significant reconstruction and rebuilding in the 18th and 19th centuries. In those centuries, it also became a popular subject for artists; Turner, Gastineau and Cotman produced sketches of the bridge and gate. In the 20th century, it suffered increasing damage as higher volumes of traffic and the use of ever-larger vehicles led to several serious accidents. In the 21st century, the construction of a new road crossing to the south enabled the pedestrianisation of the bridge.