The pound lock is a chamber with gates at each end that raises or lowers boats between two water levels, allowing canals to climb gradients and cross watersheds. The mitre-gate form was refined in Renaissance Italy and then deployed at scale on Pierre-Paul Riquet's Canal du Midi in Languedoc, a roughly 240 km waterway linking the Garonne to the Mediterranean that was completed in 1681 with over a hundred locks. The system included a summit reservoir to keep the highest reaches supplied with water. It demonstrated that long artificial waterways could overcome difficult terrain.
By making inland waterways viable freight arteries, the pound lock anchored canal-port towns and later underpinned the dense industrial canal networks that fed the growth of manufacturing cities.