Leonardo da Vinci designed a miter lock for controlling water levels in canals. A lock uses two gates and an enclosed chamber so boats can move between stretches of water at different elevations.
Leonardo’s canal-lock designs improved on simple gates by using pairs of gates that meet at an angle, forming a pressure-resistant V shape. When water presses against the gates, the force pushes them more firmly toward their meeting point. Small sluice openings allow the chamber to fill or empty in a controlled way.
Leonardo worked on canal engineering in northern Italy, including projects connected with Milan. The basic miter-lock principle was not invented from nothing by him, but his designs refined and documented it. Modern navigation locks still use the same essential sequence: close one end, equalize water levels, then open the other.