What water-powered weapon did Leonardo da Vinci call the Architonnerre?

Leonardo da Vinci called his proposed water-powered weapon the Architonnerre, commonly described as a steam cannon.

The design used a heated chamber to create pressure capable of propelling a projectile from a cannon barrel. Leonardo’s notes describe heating water and using the resulting force as an alternative to conventional gunpowder artillery.

The idea belongs to his studies of military engineering and the behavior of steam. It was an ambitious concept because Renaissance technology lacked the pressure vessels, seals, and materials needed to make such a weapon reliable and safe.

The Architonnerre should not be confused with Leonardo’s organ gun, which relied on multiple barrels, or his giant crossbow, which stored energy in a bent bow. The steam cannon was principally a pressure-based machine.