Pontcysyllte-Aquädukt, Wales

The Pontcysyllte Aqueduct (roughly pronouunced "pont-ker-SUL-ter") is a navigable aqueduct which carries the Llangollen 16 Canal over the valley of the River Dee, between the villages of Trevor and Froncysyllte, east of Llangollen 16 in north Wales. It is both the longest and highest aqueduct in Britain.

The aqueduct, built by Thomas Telford, is 1007 feet long, 11 feet wide, and 5 feet 3 inches deep. It consists of a cast iron trough supported 126 feet above the river by a bridge of 19 masonry arches. Telford had built at least one previous aqueduct from a cast iron trough (the Tern aqueduct on the Shrewsbury Canal).

The mortar used comprised lime, water and oxen blood. The iron castings were produced at the Plaskynaston Foundry, and each casting dovetails into the next. To caulk the joints, Welsh flannel was dipped in boiling sugar, after which the joints were sealed with lead.

Part of what was originally called the Ellesmere Canal, it was one of the first major feats of civil engineering undertaken by leading civil engineer Thomas Telford (supervised by the more experienced canal engineer William Jessop). The iron was supplied by William Hazeldine from his foundries at Shrewsbury and nearby Cefn Mawr. It was opened on 26 November 1805, having taken around ten years to design and construct at a total cost of £47,000.

The footpath is cantilevered over the trough, which is the full width of the aqueduct, so that narrowboats are able to move more freely through the water. There are no railings on the canal (non-towpath) side, just the edge of the trough (about 6 inches above the water level) and a sheer drop, although there are holes for railings which were never fitted.

There used to be an accessible small handle in a recess on the footpath in the middle of the centre span, the pulling of which would cause a cascade of water to tumble into the River Dee below.

The aqueduct was suggested as a contender for World Heritage status in 2005, its 200th anniversary year, and formally nominated in 2006 .