Leonardo da Vinci proposed a miter lock for canals to manage changing water levels. A miter lock uses two gates that meet in a V shape, with the point facing the higher water level.
Leonardo worked on canal engineering in Milan and studied ways to make navigation more efficient. His canal-lock designs included paired gates that could isolate a chamber between different water levels. By admitting or releasing water, boats could be raised or lowered without draining an entire canal section.
Leonardo did not invent the general idea of a canal lock, which had earlier examples in China and Europe. His contribution was refining designs and applying detailed mechanical and hydraulic thinking to navigation projects. The term “miter lock” describes the gate arrangement, not a lock for securing a door. Some sources discuss Leonardo’s canal work broadly, so the answer refers specifically to the V-shaped gate design.