"2. I know, in case of the siege of a place, how to take away the water from the ditches, and to make an infinite variety of scaling-ladders and other instruments pertinent to such an expedition.
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"4. I have also kinds of cannon most commodious and easy to carry, with which to throw inflammable matters, whose smoke causes great fright to the enemy, with serious injury and confusion.
"5. I have means, by excavations and straight and winding subterranean ways, to come to any given point without noise, even though it be necessary to pass under moats and rivers.
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"8. When the operations of artillery are impossible, I shall construct mangonels, balistæ, and other engines of marvellous efficacy, and out of the common use; and, in short, according to the variety of events, I shall build various and infinite means of offence.
"9. And when it shall happen to be upon the sea, I have means of preparing many instruments most efficient in attack or defence, and vessels that shall make resistance to the most powerful bombardment; and powders and smokes.
"10. In time of peace I believe I can satisfy very well and equal all others in architecture, in designing public edifices and private houses, and in conducting water from one place to another. I can carry on works of sculpture, in marble, bronze, or terra cotta, also in pictures. I can do what can be done equal to any other, whoever he may be. Also, I shall undertake the execution of the bronze horse, which will be the immortal glory and eternal honor of the happy memory of my lord your father, and of the illustrious honor of Sforza."
The result of this letter was a summons to the court at Milan, where Lodovico, though dissolute, was proud to surround himself with the most brilliant men and women of the age. Leonardo took with him a silver lyre, made in the shape of a horse's head, designed by himself, on which he played so skilfully that the duke and his court were enchanted. "Whatever he did," says Vasari, "bore an impress of harmony, truthfulness, goodness, sweetness, and grace, wherein no other man could ever equal him." Such a union of gentleness and sincerity with genius! Who could withstand its influence!
At Milan Leonardo remained for nineteen years, and here some of his most remarkable works were done.