Leonardo da Vinci developed the miter lock, a canal device that lets boats change water levels.
Leonardo worked on canal engineering in Milan, where differences in elevation made navigation difficult. His improvements included lock gates that meet at an angle pointing upstream. Water pressure pushes the closed gates together, helping them seal the lock chamber. Small openings or sluices could then admit or release water so a boat could rise or descend.
Miter gates had appeared in earlier waterworks, but Leonardo refined their design and documented practical details for canal construction. His work is associated especially with the system of canals around Milan, including the Naviglio di Martesana.
A lock is not an aqueduct, which carries water across a gap, and it is not simply a sluice gate. The lock chamber and paired gates together allow vessels to pass between different water levels.