In collecting such a medley of ideas, Leonardo was following a practice that had become popular in Renaissance Italy of keeping a commonplace and sketch book, known as a zibaldone. But in their content, Leonardo’s were like nothing the world had ever, or has ever, seen. His notebooks have been rightly called “the most astonishing testament to the

“His insatiable curiosity, his restless leaps from one subject to another, have been harmonized in a single work,” Kenneth Clark wrote of the Mona Lisa. “The science, the pictorial skill, the obsession with nature, the psychological insight are all there, and so perfectly balanced that at first we are hardly aware of them.”