Leonardo da Vinci helped improve the mitre lock, a canal mechanism that uses a pair of angled gates to seal a waterway.
A mitre lock has two gates that meet in a V shape pointing toward the higher water level. Water pressure pushes the gates together, helping them resist leakage. When the water levels equalize, the gates can be opened and boats can pass between canal sections at different elevations.
Leonardo studied canal engineering in Lombardy, where locks were essential for navigation and irrigation. His work is associated especially with improvements to the Naviglio di San Marco lock in Milan during the late fifteenth century.
Leonardo did not invent the entire principle from nothing, and canal locks existed before his studies. His importance was in refining practical hydraulic details and applying engineering analysis to waterways. The word mitre refers to the angled meeting edges of the gates, not to a religious hat.