What armored vehicle did Leonardo da Vinci design as a covered, conical wagon?

Leonardo da Vinci designed an armored tank as a covered, conical wagon driven by internal cranks. The vehicle was intended to protect soldiers while allowing them to fire weapons through openings around its sloping shell.

Leonardo drew the fighting vehicle around 1487 for the court of Ludovico Sforza in Milan. Its rounded, turtle-like form was covered with metal plates and carried multiple light cannons. The design also included a system of gears and cranks that several men would turn from inside the vehicle.

The tank was not built for Renaissance warfare, and the surviving drawing contains a famous mechanical problem: the gearing appears to be arranged so that the wheels would turn in opposite directions. Some historians think this may have been an intentional error to keep the design from being used by rivals. It was not a modern tank, which requires an engine, tracks, and a rotating turret.