Leonardo da Vinci’s circular armored military vehicle was an armored tank design.
Leonardo drew the vehicle in the 1480s, probably while developing military proposals for Ludovico Sforza in Milan. Its conical, turtle-like shell was covered with metal plates, and several light cannons projected through openings around the perimeter. The vehicle was intended to advance across a battlefield while shielding its crew.
The design included wheels and an internal system of gears or cranks. A commonly discussed problem is that the gearing, as drawn, would make the wheels turn in conflicting directions. Some historians think this may have been a deliberate error to prevent the design from being used, although that interpretation is not certain.
Calling it a modern tank is convenient but somewhat anachronistic. Leonardo’s vehicle had no engine, and its battlefield practicality is doubtful. It is more precisely an early armored fighting-vehicle concept, combining protection, mobility, and mounted artillery.