What defensive vehicle did Leonardo da Vinci sketch with a conical armored body?

Leonardo da Vinci sketched an armored tank with a conical, turtle-like body.

His fighting vehicle appeared in a design from about 1487–1489. The wooden cover was intended to protect soldiers inside, while sloping armor could deflect incoming weapons. Several light cannons were arranged around the vehicle so it could fire in different directions.

The machine was supposed to move with cranks operated by people inside, turning wheels through a system of gears. A famous drawing contains a gear arrangement that would not work as shown, leading to the idea that Leonardo may have deliberately introduced a flaw to prevent the design from being copied. The vehicle was never built or used in battle. Calling it a modern tank is convenient, but it had no engine, tracks, or practical field demonstration like twentieth-century tanks.