What military machine did Leonardo da Vinci sketch with a conical armored cover and cannons?

Leonardo da Vinci sketched an armored tank with a conical protective cover and cannons.

His fighting-vehicle design appears in drawings from about 1487–1489, probably made while he was seeking work from Ludovico Sforza in Milan. The vehicle resembles a covered, circular platform with sloping armor and several guns projecting around its edge. It was intended to move across a battlefield while protecting the crew inside.

The design is commonly called Leonardo’s tank, but it was never built for Renaissance warfare. The surviving plan also contains a famous mechanical problem: the internal gears appear arranged so that the vehicle would move backward rather than forward. Historians debate whether that was an error, a deliberate sabotage feature, or simply an incomplete sketch.