From 1514 to 1516 Leonardo lived in Rome and worked under the patronage of Prince Giuliano the Magnificent, brother of Pope Leo X. Giuliano was fascinated by mechanical devices and Leonardo built many toys and machines to amuse him. Among them was a machine to turn copper metal into strips of uniform size. He also completed another great painting of John the Baptist as a young man.

Leonardo had wished to keep studying human anatomy, but the Church would not allow him to examine and cut up dead bodies. Instead he studied animal parts obtained from a butcher's shop. From these he produced brilliant models of how the heart works.

In Rome he also studied optics, and he attempted to make giant, rounded mirrors in his workshop. They were similar to the mirrors used in modern telescopes, and some scholars think he hoped to observe the moon and stars.

Leonardo also studied botany, and he observed that the same patterns exist in many natural things. For example, the rings in a tree trunk resemble the ripples made by a stone dropped in water. He was always happy when repeating patterns appeared in nature, because they showed evidence of universal natural laws. Modern scientists continue to discover such patterns, often at a microscopic level, and Leonardo would certainly have been thrilled.