Leonardo da Vinci used miter gates in canal designs around Milan.
A miter gate consists of two leaves that meet at an angle pointing upstream. Water pressure pushes the leaves together against their central seam, helping the gate resist the force of the water. This arrangement became a defining feature of navigation locks and is still widely used.
Leonardo worked on Milan's canal system and is strongly associated with improvements to lock engineering, especially at the San Marco lock. His notebooks show careful studies of gates, channels, water flow, and mechanisms for controlling water levels. The lock allowed boats to pass between sections of canal at different elevations.
Leonardo did not invent the basic canal lock from nothing; locks and related water-control systems existed before his work. His importance lies in observing, refining, and documenting engineering solutions with unusual precision. A common mix-up is to call every Renaissance water gate a sluice: a sluice mainly regulates flow, whereas a lock's miter gates form a chamber that raises or lowers boats.