Leonardo da Vinci designed a steam cannon, commonly called the architonnerre, that used heated water and steam to propel a projectile.
The concept appears in Leonardo’s military notebooks. A metal tube would be heated, and water introduced into the chamber would produce expanding steam. The pressure was intended to force a cannonball out of the barrel. Leonardo’s proposal reflects his interest in using heat, pressure, and mechanical force in unusual ways.
The architonnerre was not a conventional gunpowder cannon. Historical descriptions of the design are brief, and there is no reliable evidence that Leonardo built a working example. Its operation is therefore best understood as an early steam-powered artillery concept rather than a proven battlefield weapon.
The idea is notable because it applies steam pressure to artillery long before steam engines became practical industrial machines. It should not be confused with later steam cannons or with ordinary Renaissance firearms.