The architect Francis Thompson dressed the pylons at either end as barbicans, with crenellated turrets, arrow slits and bartizans to complement the adjacent Conwy Castle.

[2] The line would improve transport and communications in the region and speed up traffic between London and Ireland as part of the national rail network that was under development.

[2] Several different cross sections were built including a one-sixteenth scale model of the Britannia Bridge, 23.8 meters in length fitted with a rectangular-section tube.

For additional support, timber piles were driven at the south east corner of Conwy Tower where the masonry is seated on a wooden platform roughly 600mm below the low water level.

[2] The project's architect, Francis Thompson, dressed the pylons at either end as barbicans with crenellated turrets, arrow slits and bartizans to complement the adjacent Conwy Castle that had stood on the promontory since the late 13th century.

[2] As designed, the tubes were to be elaborately decorated meant to resemble castle walls with machicolated cornices, stringcourses and loopholes.

The tubes are made of 16mm riveted wrought iron with cellular roofs and bases, and sheeted sides; each one weighs roughly 1,320 tonnes.

[2] Once completed onshore, they were attached to pontoons, floated along the river and jacked into position between the abutments; steam-powered hydraulic engines lifted the bridge elements into place.

[2][5] During 1899, the tubular sections were reinforced with cast iron columns to reduce the load on the span across the river to accommodate the increasingly heavy trains being used on the route.

[6] In September 1950, Conwy Tubular Bridge was recognised as being a Grade I listed structure; it is also a scheduled monument (CN167), protecting it as a historical asset for the nation.