Leonardo da Vinci designed an armored fighting vehicle commonly called Leonardo's tank.
The vehicle appears in Leonardo's notebooks from the late 15th century. Its conical armor was intended to deflect incoming projectiles, while a ring of internal wheels would move the vehicle across a battlefield. The design also included openings for cannons around the lower perimeter.
It is often called the world's first tank, but that description needs context. Leonardo's machine was a paper design, not a completed, operational armored vehicle. Its proposed mechanism also contains a likely technical problem: the gearing as drawn would make the wheels turn in conflicting directions unless corrected.
The design belongs to Leonardo's broader work for military patrons, who valued fortified machines, artillery, bridges, and other battlefield devices. Modern tanks appeared centuries later, during the First World War, and used engines, tracks, and manufactured armor unavailable to Leonardo.