Leonardo da Vinci designed canal locks to let boats pass between canal sections at different levels.
A lock is a chamber with gates at both ends. To raise a boat, water enters the chamber until its level matches the higher section; to lower it, water drains until the level matches the lower section. This allows navigation through a change in elevation without building an entire canal at one level.
Leonardo worked on canal engineering in northern Italy and is associated with improvements to lock mechanisms used around Milan. His work built on earlier canal technology rather than inventing the basic idea from nothing. A canal lock is also different from a water wheel, which extracts energy from moving water, and an aqueduct, which carries water across an obstacle.