Leonardo da Vinci developed a miter lock mechanism to help boats overcome changes in canal water level.
A miter lock uses two gates that meet at an angle, with the point facing the higher water. Water pressure helps press the gates together, improving the seal. By filling or emptying the lock chamber, boats can move between different levels without being lifted by a crane or dragged over land.
Leonardo worked on canal engineering in northern Italy, especially problems involving navigation, water control, and transport. His designs helped refine practical arrangements for gates and chambers, although canal locks had earlier precedents and were not invented from nothing by Leonardo.
The key distinction is between a lock and a simple dam or weir. A lock temporarily holds a boat in a chamber while the water level changes; a weir primarily controls or raises water without providing that same enclosed passage.