Leonardo da Vinci designed a canal lock to control water levels between connected waterways.
A canal lock lets boats move between sections of water at different elevations. Gates close a chamber, and water is admitted or released until the boat reaches the level of the next section. Leonardo's work on canal engineering included designs for a mitre gate, a pair of gates that meet at an angle and resist water pressure when closed.
His studies were closely connected with Milan's canals and with plans to improve navigation around the city. The Naviglio di San Marco lock in Milan is traditionally associated with Leonardo's engineering work, although the history of the canal system involved many engineers and stages of construction.
Leonardo did not invent the general principle of water-level control from nothing. Earlier canal locks existed in Europe and China. His importance lies in refining, documenting, and applying sophisticated lock and canal ideas during the Renaissance.