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 feet wide and is the longest aqueduct in Great Britain as well as the highest canal aqueduct in the world. A towpath runs alongside the watercourse on one side.