To Sforza

Eccellentissimo Signore mio Duca,

I write to render account of the great horse, il cavallo, that your Excellency desired should stand above the memory of your father, and to tell you plainly where the work stands and where it does not, for I have learned that a duke is better served by the verb that keeps its promise than by the verb that decorates the morning.

The model in clay is made. This your eye has seen — twelve braccia at the withers, the near foreleg lifted as a living thing lifts it, the whole mass balanced upon three points and the tail, which is more cunning than the casting men suppose, for it is the tail that carries what the legs cannot. Men came from the courtyard and stood beneath it as beneath an arch, and were silent. I tell you this not for praise but because silence is the only true measure of a thing’s size.

Now the difficulty, which I will not soften.

To cast a horse upright and entire, in one pour, as the ancients are said to have done — I do not believe it can be done without the bronze cooling unevenly and tearing itself in the cooling. I have studied the matter through many nights. My proposal is this:

— to cast the horse upon its side, the mould laid down, that the metal may run level and the heat be governed; — to build not one furnace but several, opening together, tutte in un punto, so the bronze arrives as one river and not as many quarrelling streams; — to make the outer mould in pieces bound with iron, that it may be opened and the surface corrected where the metal has failed it, for it will fail in places, and the man who promises otherwise has never poured.

What I require of your Excellency is the bronze itself — near two hundred thousand pounds, by my reckoning, and the reckoning is honest, not the flattering small number that begs the commission and then betrays it. I know the times press upon you, and that bronze is also the metal of cannon, and that a duke must choose between the horse that endures and the gun that defends the city that would house the horse. This choice is yours and not mine; I set the figures before you only so that the choice is made in light and not in the dark of my silence.

Give me the metal and the furnaces, and I will give you the thing that men ride to see from other lands. Withhold it, and the clay will wait, patient where I am not, until the season turns.

I keep, besides, the books your Excellency knows of — the canals of the Naviglio, the locks that lift the water as a man lifts a child, by stages and not by force. Of these I will write separately, that this letter not become a market of too many goods at once.

The light here is failing earlier than my hand wishes. I commend the horse and the canals and myself, in that order of usefulness, to your judgment.

Di vostra Eccellenza servitore, Leonardo da Vinci.