The Toy Zone has pictures and descriptions of fifteen weapons or defensive systems that historians have found sketched in the notebooks of Leonardo Da Vinci. These include a tank, cluster munitions, and mobile walls. The picture above is of a pivoting radial barrage canon found in the Codex Atlanticus.
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and basicly all they do is bring his war machines to life.
The main reason why Da Vinci made so many drawings for weapons was because in those days his art didn't always sell that well. And because the Masters with the Cash mostly were doing battle (most of the citystates had wars with eachother), it completely made sence to advertise knowledge of how to make incredible invincible superweapons that could inspire fear into the opponent and give the user status, glory and an edge in battle.
Da Vinci must have had an agressive note in his personality. Mona Lisa one day and tanks and giant crossbows the next.
As for Fortress...Minas Tirith, anyone?