What steam-powered cannon did Leonardo da Vinci call the Architonnerre?

Leonardo da Vinci called his proposed steam-powered cannon the Architonnerre.

The Architonnerre was a concept for launching a projectile by heating water in a sealed metal vessel. The resulting steam pressure would force the projectile from a barrel. Leonardo described the device in his military-engineering studies, presenting it as a powerful alternative to conventional gunpowder artillery.

The name combines terms associated with archery and artillery. The design is often described as an early steam cannon, although it was never demonstrated as a practical battlefield weapon and its historical operation remains uncertain.

It is important not to confuse the Architonnerre with later steam guns, which were developed by other inventors. Leonardo's proposal belongs to the experimental history of artillery and shows his interest in using heat and pressure as sources of mechanical force.