Leonardo da Vinci designed a miter lock to help boats move between waterways at different water levels.
A miter lock uses two gates that meet at an angle pointing upstream. Water pressure pushes the gates together, helping them seal the chamber. Leonardo studied this type of canal engineering while working on water-management projects in northern Italy.
The lock chamber could be filled or emptied so a boat rose or descended gradually instead of attempting to travel directly between different elevations. This made canals more useful where terrain prevented a level route.
Leonardo is sometimes credited with inventing canal locks, but earlier forms existed before his work. His contribution was the study and improvement of lock mechanisms, gates, canals, and water flow rather than the creation of the entire idea from nothing.