The Pontcysyllte Aqueduct is a navigable aqueduct that carries the Llangollen Canal across the River Dee in the Vale of Llangollen in northeast Wales.

The 18-arched stone and cast iron structure is for use by narrowboats and was completed in 1805 having taken ten years to design and build. 

It is 12 ft (3.7 metres) wide and is the longest aqueduct in Great Britain and the highest canal aqueduct in the world. A footpath runs alongside the watercourse on one side. 

The aqueduct was designed by civil engineers Thomas Telford and William Jessop for a location near an 18th-century road crossing, Pont Cysyllte. 

After the westerly high-ground route was approved, the original plan was to create a series of locks down both sides of the valley to an embankment that would carry the Ellesmere Canal over the River Dee.

The structure is a Grade I listed building and a UNESCO World Heritage Site.

According to en.wikipedia