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History of Vegetarianism - Leonardo da Vinci (1452-1519)
Italian painter, sculpture, architect and engineer; the most versatile talent of the Italian Renaissance. His most famous painting include The Virgin of the Rocks (1483-85), the Mona Lisa (or La Gioconda, 1503) and The Last Supper (?1495-97). His numerous drawings, combining scientific precision in observation with intense imaginative power, reflect the breadth of his interests, which ranged over biology, physiology, hydraulics and aeronautics. He invented the first armoured tank and foresaw the invention of aircraft and submarines. Collins English Dictionary
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Leonardo da Vinci's Ethical Vegetarianism a detailed study by David Hurwitz

. . . To this difficulty we have to add another one: the scarce or no importance which biographers pay to the eating habits of the people they write about. So for example Colin Spencer complains in his book The Heretics Feast that among 60 biographies about Leonardo Da Vinci only two of his biographers mention that he was a vegetarian. - Professor Luis Vallejo Rodríguez, Spain

from The Extended Circle by Jon Wynne-Tyson. Direct link:

Truly man is the king of beasts, for his brutality exceeds theirs. We live by the death of others: We are burial places! - from da Vinci's 'Notes'

[note: the following quote is from a work of fiction written by Merijkowsky in the 1920s - it has been established that this is not an authentic quote. The attributions for the quote above and the one below were interposed in Jon Wynne-Tyson's book - and have been misquoted ever since.]
I have from an early age abjured the use of meat, and the time will come when men such as I will look upon the murder of animals as they now look upon the murder of men. - Merijkowsky, Romance of Leonardo da Vinci

Nothing will be left,
Nothing in the air, nothing under the earth, nothing in the waters.
All will be exterminated.
- from da Vinci's 'Notes'