Llangollen is a small town in Denbighshire, north-east Wales, situated on the River Dee and on the edge of the Berwyn mountains. The Llangollen Canal is a navigable canal crossing the border between England and Wales. The canal's most notable feature is the Pontcysyllte Aqueduct built by Thomas Telford in 1805. The aqueduct is more than 980 ft long and 125 ft above the valley floor. It has nineteen stone arches, each with a forty-five foot span.