What is "architonnerre"

The Architonnerre ( Architronito) was a steam-powered cannon, a description of which is found in the papers of Leonardo da Vinci dating to the late 15th century, although he attributes its invention to Archimedes in the 3rd century BC.

Leonardo's description was hidden amongst his papers until it was rediscovered by Étienne-Jean Delécluze of the French Institute in 1838 and published in the magazine L'Artiste in 1841, well after the modern high pressure steam engine had been independently invented.