Creative crossings

 

Whether ancient stone piles or modern concrete pylons, bridges never lose their dramatic visual appeal. Mary Mulvihill looks at Ireland's proud legacy of bridge-building, which goes back more than 1,000 years.

What is it about bridges that makes them so much more interesting than the roads they connect? Their visual impact? The fact they leave the ground and take to the air? Or their individual design, which gives each one a distinct personality?

Maybe their importance is rooted in their past military significance, although today, in time of peace, we probably register this merely as convenience. For at their most fundamental, bridges overcome obstacles; whether crossing river or ravine.

Consider where we would be without them: before the River Liffey was bridged, for instance, at the mudflat that would later become Dublin, anyone wishing to cross had to wait for low tide, and then wade across, keeping to the wattle "carpet" to avoid the mud.

But what is useful in time of peace becomes a strategic target in time of conflict. So castles are built to defend bridges, battles are waged for them and cities grow around them. Horatio on the bridge at Rome; the 1691 siege of Athlone at the strategic Shannon crossing; the bridge too far at Arnhem . . . it's hard to name any road with the same historic importance.

Bridges are freighted with cultural and symbolic significance. We welcome "bridge-building" and "bridge-builders". We feature bridges on our euro banknotes. We celebrate them in song, story, and even TV documentary; witness BBC2's recent programme hailing the Brooklyn Bridge as one of the seven wonders of the engineering world.

Bridges may be short in Ireland (the longest of them a few hundred metres), but they give architects more scope for artistic expression than 100 kilometres of motorway: the beauty, brevity and elegance of an engineering sonnet, set against the long prose essay that is the road.

Nowhere in Ireland is this contrast more obvious than in the new Dublin-Dundalk motorway. Travel this route, and you will remember not the sweep of the road through the countryside, but the soaring elegance of the new Boyne bridge.

Who'd have thought a concrete pylon could be so pleasing? Dominating the skyline, and already an iconic landmark, it is as much an artistic monument as Dublin's Spire, and the Irish design team of Roughan and O'Donovan (also responsible for Dundrum's new Luas bridge) may take a well- earned bow.

This latest of Irish bridges joins some 30,000 others around the country (excluding the countless small structures, with a span of less than six feet, that are considered culverts).

We have bridges made of wood and rope, stone and brick, metal and concrete, and even glass. There are skew bridges and straight bridges, flat and humpbacked ones, lifting and swing bridges, masonry arch and clapper bridges, suspension and cable-stayed bridges . . . you name them, we have them.

Bridge-building in Ireland goes back some 1,200 years, to AD 804, the date of the country's earliest recorded bridge. This was an oak walkway, laid between upright supports, which spanned the mighty Shannon at Clonmacnoise as part of the ancient trans-Ireland highway that was the Eiscir Riada. The remains were found in the Shannon 10 years ago by divers, and thanks to tree-ring dating, we now know the year when the trees were felled.

Timber bridges were probably common in medieval Ireland, but sooner or later most were replaced by stone structures. Strangely, there is no bridge at Clonmacnoise now. Many other foot and road bridges replaced earlier fords and ferries.

The Normans, those master stonemasons, brought the art of stone bridge- building to Ireland when they landed in 1169. There are several unproven claims to the country's oldest surviving stone bridge, notably Abbeytown bridge near Boyle, Co Roscommon, possibly built around 1200, and still in use.

Although we have a precise chronological date for Clonmacnoise's now-vanished timber bridge, we lack comparable information for most other Irish bridges, because all details were lost when the Public Records Office burned in 1922. Most engineering historians agree, however (and watch for all the qualifications here), that Ireland's oldest confirmed, surviving, complete and unaltered bridge is at Trim, Co Meath, built over the Boyne in 1393 and still in use. (Earlier Boyne bridges were destroyed by the great flood of 1330, although one arch survives from Babe's Bridge, built circa 1210.)

Our two oldest surviving documented bridges are those over the Liffey at Kilcullen, Co Kildare and over the Barrow at Leighlinbridge, Co Carlow, which were built in 1320, but have since been widened for traffic. Part of Slane bridge may also date to the 1300s, but most of its 13 arches were built later.

Other noteworthy Irish bridges include Co Mayo's clapper bridge, Lisdoonvarna's spectacle bridge, Mizen Head's concrete footbridge, and the engineering triumph that is Drogheda's railway viaduct.

Clapper bridges (from the Latin claperius meaning "pile of stones"), are the simplest and oldest of bridge designs. They are rare in Ireland, but Bunlahinch ford in Co Mayo boasts a fine example that could be medieval. Made from large limestone slabs laid on rough stone piers, it forms an elevated footpath, running above a stream; the minor road alongside the bridge also fords the stream.

Lisdoonvarna's spectacle bridge (built 1875) is named for its two "eyes": the Aille river flows through the lower eye. The upper one was inserted to lighten the structure, otherwise this road bridge would probably collapse under its own weight.

The elegant footbridge leading to Mizen Head fog signal station is an engineering gem; a prefabricated reinforced concrete suspension bridge, it was the largest of its kind when built in 1909, and possibly the first to use precast elements (everything was cast on-site using sand crushed from local rock). This narrow bridge spans nearly 100 metres across a chasm that drops 100 metres to the waves below, and all the station's supplies were ferried across, often in wheelbarrows.

Drogheda's Boyne railway viaduct opened in 1855. The final link in the Dublin-Belfast line, it was considered a wonder of the engineering world: to minimise the structure's weight, the engineers chose a novel lattice-work of wrought iron girders. When completed, the bridge was the longest of its kind of the world, at 155 metres. (In 1932, the wrought iron lattice was replaced by a steel version).

To these we can now also add the soaring double harp that is Dublin's new James Joyce bridge over the Liffey. Designed by Antonio Calatrava Valls, Barcelona's noted architect/engineer/ artist, and opened earlier this year, it is a delight to the eyes, even of those who never notice bridges.

Bridge: for the record.

Oldest recorded bridge: built over the Shannon at Clonmacnoise, AD 804.

Oldest surviving arch: the remains of Babe's Bridge over the Boyne at Donaghmore; built about 1210, not in use.

Oldest surviving, complete and unaltered: Trim bridge over the Boyne, built 1393, and still in use.

Oldest surviving documented: over the Liffey at Kilcullen and over

the Barrow at Leighlinbridge, built in 1320.

Oldest iron: Dublin's Ha'penny bridge, built 1816.

Oldest suspension: Birr Castle's bridge

over the Camcor river, built 1825.

Longest road: the sweeping 521-metre Foyle road bridge between Derry and Co Donegal, built 1984.

Longest single-span stone arch: the 33-metre arch of the Lucan bridge over the

Liffey.

Only public rope bridge: at Carrick-a-rede, erected anew each summer.

Ireland's Bridges, by engineering historians Ron Cox and Michael Gould, is published this month by Wolfhound Press. See also, Michael Barry's Across Deep Waters: Bridges of Ireland (Frankfort Press, 1985)

Mary Mulvihill's award-winning book, Ingenious Ireland, is published in the UK and US this month by Simon & Schuster