Leonardo da Vinci is widely known for his many engineering designs centuries before anyone else came up with similar ideas. He was a respected artist and inventor, but also was a gifted military engineer. Something that he really understood was the psychological impact of weaponry. Da Vinci came up with several versions of a giant crossbow, comprised of winding gears similar to the compound longbow of today. When his sketches came to life on the battlefield, they spanned 27 yards across. Each device had six wheels for stability and mobility, and the crossbow itself was made of thin, flexible wood. Priming the giant crossbow involved cranking back various gears and loading up the artillery, and any projectile was launched by releasing a holding pin by striking it with a mallet. The crossbow invention appeared to be made to launch large stones or flaming bombs rather than oversized crossbow bolts, which makes it clear that da Vinci meant for this military invention to cause fear amongst enemies rather than merely inflict mass damage and chaos.

Sources:

“Giant Crossbow.” Leonardo Da Vinci's Giant Crossbow Invention, 2008, www.da-vinci-inventions.com/giant-crossbow.aspx.

“Leonardo - Giant Crossbow.” BBC Science & Nature, 2014, www.bbc.co.uk/science/leonardo/gallery/crossbow.shtml.

Image Source : Leonardo da Vinci (https://commons.wikimedia.org/wiki/File:Leonardo_da_vinci,_Giant_Crossbo...), "Leonardo da vinci, Giant Crossbow", marked as public domain, more details on Wikimedia Commons: https://commons.wikimedia.org/wiki/Template:PD-old.