Britannia Bridge is a bridge in Wales that crosses the Menai Strait between the Isle of Anglesey and city of Bangor. It was originally designed and built by the noted railway engineer Robert Stephenson as a tubular bridge of wrought iron rectangular box-section spans for carrying rail traffic. Its importance was to form a critical link of the Chester and Holyhead Railway's route, enabling trains to directly travel between London and the port of Holyhead, thus facilitating a sea link to Dublin, Ireland.

The Menai Strait is a strait which separates the island of Anglesey from Gwynedd, on the mainland of Wales. It is situated between Caernarfon Bay in the south-west and Conwy Bay in the north-east, which are both inlets of the Irish Sea. The strait is about 25 km (16 mi) long and varies in width from 400 metres (1,300 ft) between Fort Belan and Abermenai Point to 7.5 kilometres (4.7 mi) between Puffin Island and Penmaenmawr. It contains several islands, including Church Island, on which is located St Tysilio's Church.