What Leonardo da Vinci military vehicle is commonly described as an early tank?

Leonardo da Vinci’s armored vehicle is commonly described as an early tank. His design, drawn in the 1480s, resembles a conical turtle shell covered with metal plates and fitted with guns around its perimeter.

The vehicle was intended to advance toward an enemy while protecting soldiers inside. A crew would turn internal cranks connected to wheels, theoretically moving the machine in any direction. Historians have noted a deliberate flaw in the famous drawing: the crank arrangements would make the wheels rotate against one another, so the vehicle could not move as shown.

Some researchers think the error may have been intentional, allowing Leonardo to conceal military information from potential patrons or rivals. The design was never built for Renaissance warfare. Modern replicas have corrected the gearing and demonstrated that a similar armored platform can be made mobile.