One of the fundamental components of Brunelleschi's machines was the screw, which went on to find extensive applications in Leonardo's earliest technical projects. The screw also recurs in his many devices for raising water. In these studies, Leonardo combines the machine with the vital forces of nature—in particular, flowing water, whose spiral motions he saw as the natural equivalent of the screw. The plans for an automatic roasting spit and a file-making machine attest to the strictly practical aims of this early phase.
The letter to Ludovico
In 1482, Leonardo moved to Milan, where he was employed for nearly twenty years by the Duke, Ludovico Sforza. In the letter offering his services to the Duke, Leonardo made much of his technical skills. In his words: «I know how, when a place is besieged, to make endless variety of bridges, and covered chariots and ladders. Again, I have kind of mortars easy to carry; and with these I can fling small stones almost resembling a storm. And if the fight should be at sea I have kinds of many machines most efficient for offence and defence; and vessels which will resist the attack of the largest guns. I will make covered chariots, safe and unattackable, which there is no body of men so great but they would break them. In case of need I will make big guns and mortars of fine and useful forms, out of the common type. I would contrive catapults and other machines.»
Leonardo in Milan
The record of Leonardo's work in Milan survives not only in loose manuscript sheets (as for his earlier years) but in bound collections known as "codices." Many of his studies can be properly described as "technological dreams." Meanwhile, Leonardo embarked on a thorough analysis of waterways, which played a vital role in the Duchy of Milan. The encounter with Francesco di Giorgio in Pavia in 1490 was a decisive moment in Leonardo's training.
In about 1490, Leonardo planned to write a "treatise on water," which he viewed as a necessary first step toward solving hydraulic-engineering problems. Likewise, he saw anatomy as the indispensable basis for the representation of the human body. Leonardo was trying to reverse the empirical approach of the workshop tradition. For him, geometry was an instrument capable of unifying diverse fields of research, from mechanics to botany, and from hydraulics to anatomy. At the same time, Leonardo studied Latin and steeped himself in classical learning. However, many of his technical researches in these years are still attempts to solve specific real-life problems, such as the studies on casting a bronze horse for the Sforza monument.
After MilanIn 1499, the French army toppled the Sforzas, and Leonardo left Milan. In 1500, he was in Venice with Luca Pacioli, who was largely responsible for his training in mathematics and geometry. The following year, he was in Florence, where he concentrated on studying geometry. In 1502, he left Florence to work as military engineer for Cesare Borgia—the notorious Duke of Valentinois—then waging war in central Italy. For strategic purposes, Leonardo prepared the extraordinary map of Imola. In 1503, he was back in Florence, which was at war against Pisa. Leonardo came up with a plan to deviate the course of the Arno in order to flood the enemy town. During this period, he also compiled the Codex on the Flight of Birds.
The final years
In 1508, Leonardo left Florence for good. His penchant for theory intensified in his last years. He studied mechanics, anatomy, and geology in a closely interlinked manner, regarding them as governed by universal laws. He conceived the human body as a set of perfect mechanisms. Geometry was an abiding interest. Leonardo was particularly fascinated by the transformations of the surfaces of geometric shapes, which he applied to hydrology and to studies of the heart. In 1513, he moved to Rome, where he prepared projects for draining the Pontine Marshes and designed rope-making machines. In 1516, Leonardo accepted the invitation of King Francis I and moved to France, where he was venerated as a "very great philosopher." He died in Amboise on May 2, 1519.