If you look at one of Leonardo da Vinci's sketches, there is a so-called circular tank with cannons attached on all sides and wooden panels covering it to protect the occupants. It moves by human power.
Similarly, among the weapons designed by Conrad Kyeser, a medieval European engineer, there is a vehicle moved by horses, which is also surrounded by walls and equipped with hand cannons and blades.
Unlike the two examples above, the Wagenburg (war wagon) was a weapon that was actually used, employed to form defensive formations to protect friendly forces.
In any case, there has been a constant demand for "moving fortresses" that protect allies from enemies while maintaining mobility.
Since the most advantageous battle is a defensive one, the idea was that if that "fortress" could move, one could fight advantageously against enemies anywhere.
