Perspective view of a part of the Iron Aqueduct which conveys the Shrewsbury Canal over the River Tern at Longden in the County of Salop

Longdon-on-Tern, the first cast iron aqueduct, opened to traffic in 1796, carrying the Shrewsbury canal over the River Tern. Cast iron avoided the need for great thicknesses of puddled clay to seal the canal trough, resulting in smaller, lighter structures.