Leonardo da Vinci sketched a tank-like armored vehicle powered by people turning internal cranks.
Leonardo designed the fighting vehicle around 1487 for Ludovico Sforza, the ruler of Milan. Its conical armored shell was covered with metal plates and fitted with guns around the lower edge. The vehicle was intended to move across a battlefield while protecting its crew from enemy fire.
The machine was driven by four men operating cranks inside the structure. A famous drawing appears to show a gearing problem that would prevent the wheels from turning correctly. Historians debate whether this was an intentional error to keep the design secret or simply a drafting mistake.
It was never built as a fifteenth-century combat vehicle. Calling it a modern tank is a convenient comparison, but Leonardo's design lacked an engine, turret, and many features associated with twentieth-century tanks.