He kept notebooks full of ideas about architecture and technology of all kinds. Even the doodle pictures of parachutes he drew in the margin of his notes turned out to be technically perfect designs. He drew up plans for an assault battleship, a construction crane, a trench-digging machine, a revolving bridge, and a deep-sea diving suit. He made architectural sketches of churches that looked like seashells or blossoming flowers, none of which got built because they were too impractical. Most of his ideas were too ambitious for the tools that existed at the time.

In 1482, Leonardo began a sculpture of a horse. It was extremely difficult to design because the final product would weigh many tons when cast in bronze, and Leonardo wanted the horse to be rearing back on its hind legs. He spent 11 years sketching out the solution to the problem of the horse’s balance, but when he tried to cast the horse in bronze, he found that all the bronze in the city had been used to build cannons for an impending war. So the sculpture went unfinished until 1999, when a Japanese-American sculptor used Leonardo’s drawings and plans to build the horse. The finished product was 23 feet high, weighed 15 tons, and was perfectly balanced.

In 2001, builders completed a Leonardo da Vinci bridge supported by huge rings outside of Oslo, Norway.

Leonardo is best known for his painting the Mona Lisa, which is generally considered the most recognizable work of art in the world. He kept it with him for most of his life, working on it now and again. Today, it is probably the most analyzed work of art in history. For centuries, scholars have tried to determine the identity of the woman in the painting. A computer graphics consultant analyzed the painting and found that the nose, mouth, forehead, cheekbones, and eyebrows all lined up with a portrait Leonardo painted of himself. So he may have used himself as the model.