the span of the river. Stephenson also deployed the tubular bridge on a larger scale across the Menai Strait between Anglesey and the Welsh mainland, in what was the Britannia Bridge. While developing the design which was made of wrought iron, Stephenson consulted William Fairbairn (who had extensive experience in working with iron), the mathematician Eaton Hodgkinson and resident engineer Edwin Clark. During February 1846, the men presented their design to the company who approved further development and experimentation to validate the design. 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. Testing incorporated various conditions, including wind and temperature variations. The designs for both the Conwy Railway Bridge and Britannia Bridge were similar. Construction During May 1846, groundwork for the bridge commenced. On either shore, the underlying bedrock was levelled close to the river's low water level for the foundations of the towers. 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. 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. As designed, the tubes were to be elaborately decorated meant to resemble castle walls with machicolated cornices, stringcourses and loopholes. The fitting of external decorations was abandoned on the grounds of expense and extra weight. The bridge contractor was William Evan. The ironwork was constructed by Easton & Amos. On 15 June 1846, the foundation stone of the towers was laid. The towers accommodated entrance portals within twin arches, through which the railway are carried into the tubes. The tubes are made of 16mm riveted wrought iron with cellular roofs and bases, and sheeted sides; each one weighs roughly 1,320 tonnes. The tubes, which are 129.2 meters long and 4.4 meters wide, were constructed using shipbuilding techniques. 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. On 6 March 1848, the first tube was floated; its installation took nine days to complete. Operational life The bridge was officially opened in 1849, although the first