On Painting – Leon Battista Alberti by Leon Battista Alberti

"The painter is concerned with things that are seen."

Written in 1435, this treatise codified the principles of linear perspective for the first time. Alberti explains the geometry of visual rays, the use of color, and the composition of narrative scenes ('istoria'), arguing that painting is an intellectual pursuit worthy of the liberal arts, not just a craft.

Alberti's work is the theoretical foundation of Renaissance art. It gave artists like Brunelleschi and Masaccio the tools to create the illusion of three-dimensional depth on a flat surface, forever changing the way the Western world depicted reality.