The unique double-span shape of the bow Leonardo drew on these pages obviously involves the use of a steel bow that is difficult to bend. In traditional crossbows, the tiller, which is the main wooden loadbearing piece of a crossbow, contains the nut, a small metal ball that engages the bowstring. By pressing the trigger located below the tiller, the crossbowman activates a lever that frees the nut and makes it turn, thereby releasing the bowstring and firing the bolt. To reload the crossbow, the crossbowman had to secure the bowstring back around the nut.
The tiller of Leonardo’s crossbow, on the other hand, is divided into two parts. The bottom part, secured by a sturdy hinge, can be opened downwards. A system of levers inside the tiller brings the nut to the bowstring in its resting position; the nut engages the bowstring and then both are brought back to the loading position. By opening and closing the tiller using a lever, the crossbowman can load the crossbow without ever touching the bowstring or using external objects, thus greatly accelerating the loading process.
If this weapon had ever been realized, it would have made a major difference on the battlefield.