Shannon Bridge, Cloniffeen, Co. Offaly

What stands today is not quite any single bridge but rather the accumulated result of a ford, then a multi-arched stone structure, then an added span, then a swivel bridge, and finally a concrete replacement, all occupying more or less the same strategic point on the river.

The story begins, as so many Irish river crossings do, with a ford, a shallow passage where travellers and livestock could wade across the Shannon before any formal structure existed. Around 1700, a 17-arch bridge was constructed at this spot, a substantial undertaking that suggests the crossing was already well-used and commercially significant. Then, in 1755, the Commissioners of Inland Navigation intervened. The Commissioners were responsible for improving Ireland's inland waterways during the eighteenth century, and their addition of an extra span on the eastern bank almost certainly had to do with the practical demands of river traffic, allowing boats to pass more freely. That added span had its own successor: in 1845, the engineer Thomas Rhodes designed a cast iron swivel bridge to replace it. A swivel bridge rotates horizontally on a central pivot, opening a channel for vessels to pass through, and in the mid-nineteenth century cast iron was the modern material of choice for such a mechanism. Rhodes's design did not last indefinitely either. By 1883 to 1884 it had been replaced by a concrete span, bringing the crossing into the materials of a new era while the original 17-arch structure from around 1700 remained beside it.