Leonardo da Vinci improved the miter lock, a canal device that raises boats between different water levels.
A lock chamber is enclosed by gates at both ends. A boat enters, the gates close, and water is added or released until the chamber matches the level of the next section of canal. The boat can then leave at the higher or lower elevation.
Leonardo worked on canal engineering in northern Italy and is associated with improvements to lock-gate design, especially the use of angled miter gates. When water presses against the gates, the angled arrangement helps force them tightly together rather than pushing them open.
Leonardo did not invent the basic concept of the canal lock. Earlier pound locks existed in Europe, including in Italy and the Netherlands. His contribution belongs to the practical refinement of water-control and navigation technology, not to the creation of the entire system.