Pont Britannia (Britannia Bridge)
Map: 1889 – County Series 1:2500
To celebrate St David’s Day, Cassini has been exploring our collection of historical maps of Wales and has found one of the ground breaking engineering feats of the eighteen hundreds.
Pont Britannia (Welsh for Britannia Bridge), a bridge across the Menai Strait between the island of Anglesey and the mainland of Wales, opened on 5 March 1850. When built it had the longest continuous wrought iron span in the world.
It was originally designed and built by Robert Stephenson as a tubular bridge of wrought iron rectangular box-section spans for carrying rail traffic.
In 1840, a Treasury committee decided in favour of Railway pioneer George Stephenson’s proposals, which included the Britannia Bridge, over those of Thomas Telford and final consent for the route was given in 1845. Stephenson’s son Robert was appointed as the chief engineer.
The design required the Menai strait to remain accessible to shipping and the bridge to be sufficiently stiff to support the heavy loading associated with trains, so Stephenson decided to constructed a bridge with two main spans of 460-feet (140m) long rectangular iron tubes, each weighing 1,500 tons, supported by masonry piers, the centre one of which was built on the Britannia Rock.
Two additional spans of 230-feet (70m) length completed the bridge making a 1,511-feet (461m) long continuous girder. The trains were to run inside the tubes. Up until then the longest wrought iron span had been 31 feet 6 inches (9.6 m).
When first conceived, the tubular bridge was to have been suspended from cables strung through the openings at the tops of the towers. However, after engineering calculations and tests of the finished tubes it was decided that they were strong enough by themselves to carry the weight of the trains.
The bridge was decorated by four large lions sculpted in limestone by John Thomas, two at either end. These were immortalised in the following Welsh rhyme by the bard John Evans (1826–1888):
|Four fat lions
Without any hair
Two on this side
And two over there
|Pedwar llew tew
Heb ddim blew
Dau ‘ochr yma
A dau ‘ochr drew