What armored military vehicle did Leonardo da Vinci design with conical, sloped plating?

Leonardo da Vinci’s armored military vehicle with conical, sloped plating is commonly called Leonardo’s tank.

Leonardo designed the fighting vehicle around 1487 for the ruler Ludovico Sforza of Milan. Its shell resembled a broad, covered tortoise, with sloping armor intended to deflect enemy fire. Small cannons projected through openings around the vehicle, while crews inside would turn cranks connected to wheels.

The machine was never built for Renaissance warfare. A famous drawing contains a gearing problem that would make the vehicle move in the wrong direction if assembled exactly as shown. Historians debate whether the error was accidental or deliberate, since Leonardo may have wanted to keep a dangerous design from being used. Calling it a tank is modern shorthand: the machine was not a twentieth-century tracked tank, and its proposed wheels and human propulsion were very different from later armored vehicles.