Draft of a letter from Leonardo da Vinci to Ludovico Sforza:
Your Gracious Highness! I have sufficiently seen and tested the productions of all who are considered masters of the art of inventing war-machines. And since the working and function of these instruments is no different from that of the machines in common use, I shall endeavour -- approaching no one else -- to make myself clear to Your Excellency and reveal my secrets. I shall put them at your disposal whenever you desire and hope for good results from the things which I shall now briefly describe ...
First: I have a means of making very light bridges which can be very easily transported ... And I have others which are proof against fire and are thus indestructible in battle, easy to take down and put up again, and I also know of a means to get fire to the bridges of the enemy and destroy them. Secondly: In besieging a place I know how to cut off the water in the dikes, also how to construct many drawbridges and other apparatus necessary for such an undertaking. Thirdly: If during a siege the engines cannot be effectively used on account of the height or strength of the town wall, I have a means to destroy every tower or fortification ... Fourthly: I know of a kind of siege-engine which is very light and easy to move and which can be used hurl fire-bombs. Their smoke will terrify, confuse and severely injure the enemy. Fifthly: I know how to construct subterranean caves and winding passages which can be made without any noise ... Sixthly: I can make sound, indestructible armoured vehicles. If these reach the enemy with their cannons, they can compel the largest forces to retreat and afterwards the infantry can follow them in safety and without any let or hindrance. Seventhly: I can make, if necessary, bombards, mortars and other field-guns ... Eighthly: Where cannons cannot be used I shall construct stone-throwing machines, catapults, slings and other instruments, amazing and hitherto completely unknown ... Ninthly: If this should be necessary, I know of apparatus for use at sea for attack and defence, such as ships which can withstand the force of the strongest opponents and produce dust and smoke. In time of peace I believe I can achieve something in architecture, as well as another, both in building public and private buildings and in channelling water from one place to another. Further, I work as a sculptor in marble, bronze and clay and can paint as well as others with whom I may be compared. I could also add my labours to the bronze horse which is to contribute to the undying fame and eternal memory of your father and the renowned house of Sforza ...
Leonardo da Vinci; 'Letters of the Great Artists', p. 34-8
Leonardo da Vinci receives the Sforza commission from Ludovico Sforza, to cast the largest equestrian statue ever, in honour of Ludovico's father.
Impatient with Leonardo's delays in completing the clay model for the The Horse, Ludovico Sforza writes to Pietro Alemanni, the Florentine Ambassador to Milan, asking him to find "a master capable of doing the work."
The 66 tons of bronze which has been set aside to cast Leonardo's equestrian statue is sent instead to Ferrara to make cannons for the war against France.
The clay cast for Leonardo's equestrian statue, known as Il Colosso, is displayed at the wedding of Bianca Maria Sforza to great acclaim.
Leonardo da Vinci drops plans for the Sforza monument until it can be cast and begins reclamation work in the Sforza lands near Vigevano, freeing one vast tract of water and converting another to a grazing area.
The Horse is seriously damaged by French bowmen who use it as target practice. It may not actually have been destroyed at this date, as Vasari claims, though.
Sabba da Castiglione reports that The Horse has suffered serious damage from being used as target practise by the Gascon bowmen years earlier.
Michelangelo chances upon Leonardo da Vinci discussing Dante at Piazza della Signoria and berates him for his failure to cast The Horse.