A boat crosses a canal bridge 38 meters above

A boat travels across a river, but it floats on water through the air, 38 meters above the river. This is the Pontcysyllte Aqueduct in Wales, UK, where a 307-meter-long cast iron trough transports canal water and boats across the valley. The initially proposed low stone aqueduct method would have required locks on both sides, potentially slowing down transit, and the structure would have needed to be lightweight to span the high valley. Therefore, Thomas Telford and William Jessop opted to create a massive cast iron trough instead of building a stone waterway. They erected 19 cast iron spans on 18 slender stone piers, placed the entire canal on top, and then sealed the joints with interlocking iron plates and caulking before filling it with water for testing. Thanks to this, boats could cross the River Dee while maintaining the same water level, without the need to ascend and descend locks. Completed in 1805, this aqueduct is still in use as a canal today.