Having, My Most Illustrious Lord, seen and now sufficiently considered the proofs of those who consider themselves masters and designers of instruments of war and that the design and operation of said instruments is not different from those in common use, I will endeavor without injury to anyone to make myself understood by your Excellency, making known my own secrets and offering thereafter at your pleasure, and at the proper time, to put into effect all those things which for brevity are in part noted below--and many more, according to the exigencies of the different cases.
I can construct bridges very light and strong, and capable of easy transportation and with them pursue or on occasion flee from the enemy, and still others safe and capable of resisting fire and attack, and easy convenient to place and remove; and have methods of burning and destroying those of the enemy.
I know how, in a place under siege, to remove the water from the moats and make infinite bridges, trellis work, ladders and other instruments suitable to the said purposes.
Also, if on account of the height of the ditches, or of the strength of the position and the situation, it is impossible in the siege to make use of bombardment, I have means of destroying every fortress or other fortification if it be not built of stone.
I have also means of making cannon easily and convenient to carry, and with them throw out stones similar to a tempest; and with the smoke from them cause great fear to the enemy, to his grave damage and confusion.
And if it should happen at sea, I have the means of constructing many instruments capable of offense and defense and vessels which will offer resistance to the attack of the largest cannon, powder and fumes.
Also, I have means by tunnels and secret and tortuous passages, made without any noise, to reach a certain and designated point; even if it be necessary to pass under ditches or some river.
Also, I will make covered wagons, secure and indestructible, which, entering with their artillery among the enemy, will break up the largest body of armed men. And behind these follow infantry unharmed and without any opposition.
Also, if the necessity occurs, I will make cannon, mortars and field-pieces of beautiful and useful shapes, different from those in common use.
Where cannon cannot be used, I will contrive mangonels, dart-throwers and machines for throwing fire, and other instruments of admirable efficiency not in common use; and in short, according as the case may be, I will contrive various and infinite apparatus for offense and defense.
In times of peace I believe that I can give satisfaction equal to any other in architecture, in designing public and private edifices, and in conducting water from one place to another.
Also, I can undertake sculpture in marble, in bronze or in terra cotta; similarly in painting, that which it is possible to do I can do as well as any other, whoever he may be.
Furthermore, it ill be possible to start work on the bronze horse, which will be to the immortal glory and eternal honor of the happy memory of your father, My Lord, and of the illustrious House of Sforza.
And if to anyone the above-mentioned things seem impossible or impracticable, I offer myself in readiness to make a trial of them in your park or in such place as may please your Excellency; to whom as humbly as I possibly can, I commend myself.
A letter from Leonardo to Lodovico Sforza in 1480 or 1481. Taken from Parsons, Engineers and Engineering in the Renaissance, pp. 16-17.