What animal-inspired feature did Leonardo da Vinci include in his armored vehicle design?

Leonardo da Vinci’s armored vehicle design had a turtle-shaped body.

In a drawing from about 1487, Leonardo proposed a covered fighting vehicle with a broad, conical shell. The sloping exterior was intended to help protect occupants from projectiles, while guns would project through openings around the vehicle. The overall appearance resembles a land turtle, giving the design its familiar nickname.

The vehicle was supposed to move using cranks connected to wheels. Leonardo’s notes also indicate space for a crew inside. It is often called Leonardo’s tank, but it was not a modern tank: it had no engine, rotating turret, caterpillar tracks, or battlefield trial.

A famous detail is an apparent error in the gearing, which would make the vehicle move in the wrong direction if built exactly as drawn. Historians debate whether this was accidental or deliberate, but the design remains an important early concept for an armored fighting vehicle.