Leonardo da Vinci designed an armored tank with sloped armor and internal hand-cranked wheels.
Leonardo drew the vehicle in about 1487–1489 while working for Ludovico Sforza in Milan. Its conical, turtle-like shell was intended to protect soldiers from enemy fire. Several cannons projected through openings around the vehicle, allowing it to fire in multiple directions.
The vehicle was meant to be moved by people turning cranks connected to wheels. A famous drawing contains a mechanical inconsistency: the gears appear arranged so that the wheels would turn in opposite directions. Historians debate whether this was deliberate, an error, or a way of concealing the design from casual readers.
Calling it a modern tank is convenient but slightly anachronistic. Leonardo's vehicle had no engine and was never built for battle in his lifetime. It was an ambitious armored fighting-vehicle concept, not a working twentieth-century tank.