Leonardo da Vinci’s steam cannon was designed to fire a cannonball using steam pressure.
The weapon, commonly called the architonnerre, was a proposed Renaissance cannon that used heated water to create steam. In the design concept, a metal vessel would be heated until the resulting pressure forced a projectile from the barrel. Leonardo’s notes treated steam as a source of explosive force long before practical steam engines became common.
The architonnerre belongs to the group of military machines Leonardo sketched while working for powerful patrons and studying artillery. It was a theoretical design rather than a weapon known to have been built and tested successfully. The concept also reflects Leonardo’s interest in converting heat into mechanical or ballistic power.
It should not be confused with Leonardo’s multi-barreled cannon, which used many barrels to increase the rate of fire, or with a conventional cannon powered by gunpowder. The architonnerre’s defining feature was steam pressure generated by heating water.