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I kept daily notes and drawings, about 13,000 pages fusing art and natural philosophy, mostly in mirror-image cursive; they now sit in the Codex Atlanticus, the Codex Leicester and major libraries.

One of my notebook observations, "Il sole non si muove", four words in which I state where the Sun stands.

A line from my diary from the period of Saint Jerome in the Wilderness, an unfinished painting of a penitent whose kneeling form I tied to my anatomical studies.

I gathered my notes on anatomy, light and landscape as material for a series of treatises, so that painting could be taught as a science built on the study of nature.

My science works by observation: I try to understand a phenomenon by describing and depicting it in the utmost detail, rather than leading with experiments or theory.

In Milan I painted the Virgin of the Rocks for the Confraternity of the Immaculate Conception: four figures in a wild landscape of rock and water, finished in two versions.

For Ludovico Sforza I designed an equestrian monument to Francesco Sforza larger than Donatello's Gattamelata or Verrocchio's Colleoni, completed the model and planned the casting in detail.

In 1502 I made a town plan of Imola that won me the post of Cesare Borgia's chief military engineer and architect, then a map of the Chiana Valley for his strategic position.

Studying perpetual motion, I concluded it was impossible and in 1493 wrote down laws of sliding friction in my notebooks, two centuries before Guillaume Amontons rediscovered them in 1699.

I drew machines the way I drew bodies, producing the first form of the modern technical drawing and a perfected exploded view that shows internal components; my engineering studies fill over 5,000 pages.