I sometimes wonder if drivers using the Britannia Bridge ever appreciate the fact that they shouldn’t really be there at all. But for one of British railway architecture/engineering’s more unfortunate moments, the Britannia Bridge might well have remained what it originally was, a railway bridge pure and simple.

Straddling the Menai Strait between Anglesey and the Welsh mainland with its deck 30m or so above water, the Britannia Bridge is an impressive piece of engineering, with its steel arches supporting the two-level deck.

Impressive though it is now, the Britannia Bridge was originally a much more slender and delicate affair. Engineered by Robert Stephenson to allow the Chester and Holyhead Railway to reach Anglesey, it was one of the two big bridges that restored his reputation after the disaster at his bridge over the River Dee, as explained last week (the other was the High Level Bridge in Newcastle).

It was a fabulously ambitious piece of engineering, pushing the boundaries of what was considered achievable. The bridge was tall – the British navy wanted to be able to sail its ships underneath. It also featured just three intermediate piers, spaced 140m apart from each other. Bridging those gaps, and smaller ones between the outer piers and the bridge’s abutments, were wrought iron tubes (actually box girders). Unlike the cast iron of the Dee Bridge, the wrought iron of the tubes was able to flex sufficiently to cope with the stresses imposed by passing trains. Altogether there were eight tubes, because the railway had two tracks, and they had to be floated out into the Menai Strait – not the easiest stretch of water to work in given its fast currents – and then jacked all the way up to their resting places, where they were joined to create two very long tubes.

The Britannia Bridge opened in 1850. Slender and elegant, it was a thing of true beauty. The masonry piers were finished in a vaguely Egyptian style of architecture, very in vogue at the time, and repeated later at the Clifton Suspension Bridge on the outskirts of Bristol, but by a different engineer (hat, cigar, you know the one I mean). Four lions carved by John Thomas, two at each end of the bridge, leant further gravitas to the structure. I think you can trace the late 1940s British Transport Commission/British Railways lion-on-wheel to these lions. There is something very similar about the design of the heads, even if these lions are lying down.

The Victorians were funny about railways, often being as terrified of them as impressed. I can’t help feeling that Stephenson’s engineering solution for the Menai Bridge was not only very elegant, but avoided nervous passengers being scared witless by the sight of the water far below them. Mind you, they probably worried about being asphyxiated in the tubes instead. They were always worrying about something.

The then-extraordinary length of the wrought iron tubes was also partly the responsibility of another engineer, William Fairbairn, who Stephenson worked with on the design of the bridge. It was he who convinced Stephenson that the tubes were strong enough to span the distance. The tubes had a strengthening cellular construction at the top and bottom of the tubes, and a stiffening structures along their sides, which gave a distinctive corrugated appearance, which can still be seen at Conwy, where another (smaller) Stephenson tubular bridge survives alongside the castle.

You know that thing where children can’t resist running toy cars through cardboard tubes? Tubular bridges are fascinating for exactly the same reason. They’re a bit like tunnels, but all on show. The train pops in one end, and then you wait, and then it pops out of the other. Brilliant.

That was exactly how the Britannia Bridge worked for 120 years. With its distinctive appearance and its four lions, it became a well-known local landmark, and a well-loved piece of railway engineering by the people who care about that kind of thing (me, and probably you, unless you’ve got here by accident).

However, on the night of 23 May 1970, some teenagers got into the bridge. The exact circumstances of why they were there, and what happened next, is the subject of no little confusion. That is perhaps unsurprising given that the bridge would end up destroyed just a few hours later, which hardly encourages a full and forthright explanation.

They might have been looking for birds nests and bats (according to the official report into the fire, reproduced here), or just bats (as here) or they might have just been exploring the bridge (as here). The Daily Post reports that one of the teenagers involved said they had been invited to a party by a girl, but couldn’t get in, so went to the bridge instead. Lighting a piece of paper found there, one of teenagers said they threw it behind one of the girders, and you kind of have to wonder whether they really didn’t realise that this was almost certainly going to cause a fire. It did. The sleepers of the railway track were covered in tar (flammable), the bridge must have accumulated some burnable debris over its life, and the tubes had been waterproofed by pitch (also flammable).

Any parent, or foster carer in my case, of a teenager will recognise in this story the classic elements of a teenage adventure gone badly wrong. There’s a dramatic and thoroughly undesirable outcome, some degree of reluctance on the part of those involved to explain the precise circumstances which led up to it, and a range of possible motivations offered.

Whether you consider it accidental or not (many in the railway industry would tell you that trespassing on the railway in the first place makes you culpable  for any damage which results), the end result was that the Britannia Bridge was torched. Firefighters were hampered in their efforts to douse the flames by a lack of water at sufficient pressure, and also by the continuous tube structure of the bridge. There were no firebreaks within, and no way into the tubes from the side. The tubes acted as giant chimneys and burnt through the night.

Wrought iron is forgiving of stress, but one thing it can’t stand is intense heat. It alters the composition of the metal, robbing it of its strength. The tubes were damaged beyond repair, and had to go. A section of one of them remains alongside the bridge as a memorial.

It took two years to reopen the bridge to rail traffic, now with a single line of track instead of two, and the new design features additional (and very unsympathetic) concrete supports under the deck at the outer ends, with new steel arches built between the masonry piers. It’s now a bridge which is muscular and impressive, rather than slender and elegant. It was designed by Husband & Co of Darlington. The rebuild gave the opportunity to add a road deck above the rail deck, providing relief to the only other road bridge onto Anglesey, Telford’s Menai Suspension Bridge a little to the north-east. The installation of the new decks required the openings in the Britannia Bridge’s towers to be enlarged, and they gained some slightly clumsy lintels in the process.

The new road deck opened in 1980. One hundred and thirty years later, Stephenson’s Britannia Bridge finally matched his High Level Bridge, which is also a rail/road double-decker. Because of the height of the road deck, the four Britannia Bridge lions can’t be seen by car drivers, but they’re still there, and visible from trains. Occasionally people suggest moving them up to road level (see this, for instance) but they surely belong with the railway which gave rise to them, not to the road.

It’s a wonderful bridge, still serving its function admirably, but the original tubular bridge is one of the great losses of British railway history.

How to find the Britannia Bridge

Click here for The Beauty of Transport’s map

Bibliography and further reading

Cruickshank, Dan (2010): Bridges. Collins: London

Engineering Timelines webpage on Britannia Bridge, here

Network Rail’s Virtual Archive page for the Britannia Bridge, here

…And anything linked to in the text above.