A tubular bridge is a bridge built as a rigid box girder section within which the traffic is carried. Famous examples include the original Britannia Bridge over the Menai Strait, the Conwy railway bridge over the River Conwy, designed and tested by William Fairbairn and built by Robert Stephenson between 1846 and 1850, and the original Victoria Bridge in Montreal.

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.