As he was finishing his first round of anatomical studies, he was beginning work on what would be the greatest expression in the history of art of that maxim, The Last Supper.

He is insatiable. Over and over again, year after year, Leonardo lists things he must do and learn. Some involve the type of close observation most of us rarely pause to do.

The Arno projects, the circular fortress, and the draining of the Piombino swamps had one thing in common with many of Leonardo’s grandest projects, and even some of his less grand ones: they never came to fruition. They showed Leonardo at his most fantastical, dreaming up schemes that darted back and forth across the boundaries of practicality.