Fun fact: The man himself Leonardo da Vinci once designed a tank.

The machine was designed while Leonardo da Vinci was under the patronage of Ludovico Sforza in 1487. Sometimes described as a prototype of modern tanks, Leonardo's armored vehicle represented a conical cover inspired by a turtle's shell. The covering was to be made of wood and reinforced with metal plates that add to the thickness. Slanting angles would deflect enemy fire. The machine was powered by two large inside cranks operated by four strong men. The vehicle was equipped with an array of light cannons, placed around the perimeter.
The gears of the design were located in a reversed order, making the vehicle unworkable. This is thought by some sources to have been a deliberate mistake by Leonardo as a form of security, in case his design was stolen and used irresponsibly.
The armored vehicle was designed to intimidate the enemy rather than to be used as a serious military weapon. Due to the vehicle's impressive size, it would not be capable of moving on rugged terrain. The project could hardly be applied and realized in the 15th century.