Causey Arch
Stanley, County Durham.
Causey Arch is the oldest surviving single-arch railway bridge in the world. It carried an early waggonway (horse drawn carts on wooden rails) to transport coal over the Causey Burn.
It was built in 1725–26 by stonemason Ralph Wood. Two tracks crossed the Arch: the "main way" for coal to the River Tyne, and the "bye way" for returning the empty wagons. Over 900 horse-drawn wagons crossed the arch each day using the Tanfield Railway.
It had an arch span of 31 metres (102 ft), a record it held for thirty years until 1756 when the steeplu-humped 140 ft span Pontypridd Old Bridge was built.
Use of the Arch declined when Tanfield Colliery was destroyed by fire in 1739.
The Arch is Grade I listed. It was restored and reinforced in the 1980s.
The above information is largely condensed from the Wikipedia entry.