Leonardo da Vinci improved the miter lock by using hinged gates to control a water chamber.
A miter lock has two gates that meet in a V shape, with the point facing the higher water level. Water pressure pushes the gates together, helping them resist the force of the water. Leonardo refined this type of canal lock while working on waterways around Milan, especially the Naviglio di Martesana.
The lock chamber allowed boats to move between different water levels without forcing them to climb a ramp or endure a sudden drop. Operators could close the gates, adjust the water level, and then open the opposite gates. This made navigation possible across changes in elevation.
Leonardo did not invent every principle of canal locks; earlier systems existed in Europe and China. His importance was in improving and documenting practical hydraulic engineering. The miter-gate arrangement later became one of the standard forms used in navigation canals.