Was there a plan for how to propel the circular wooden tank design of Leonardo da Vinci's? It seems far too heavy to be powered Flintstones-style by the people inside, but it also seems too small for horses or oxen to fit within it.
In actual history the invention of the tank was tightly related to the development of the combustion engine, but it seems strange for Da Vinci to have designed a vehicle he had no idea how to move. Designing a glider that can't glide is one thing, (flight was a totally new idea and thus a tough nut to crack), but "it's too heavy" should have been a fairly glaring error for a vehicle designer.
Did Da Vinci have an idea for how his tank would move? Or was it an incomplete design for that very reason?