What cannon concept did Leonardo da Vinci call the Architonnerre?

Leonardo da Vinci’s Architonnerre was a steam-powered cannon concept.

Leonardo described the Architonnerre in military-engineering notes as a weapon that would use heated water to create pressure. The pressure would force a projectile from a barrel, offering an alternative to conventional gunpowder artillery. His account involved heating a container and directing the resulting force toward the cannon chamber.

The concept is important because it connects Leonardo’s interest in weapons with his experiments in heat, pressure, and mechanical power. It should not be treated as evidence of a successful working steam cannon. The surviving description is a design proposal, and historians debate how practical its construction and firing would have been.

The name can cause confusion because Leonardo designed many artillery devices. The Architonnerre is identified by its proposed use of steam or expanding heated water, not by springs, compressed air, or rotating gun barrels.