Leonardo da Vinci's Mona Lisa is the world's most visited artwork. Its appeal rests partly on several mysteries.
Leonardo's obsession with water flowed through his technical work, his art and his scientific ideas.
Leonardo's professional life reveals his genius for creating technologies of destruction.
His exquisite drawings suggest a particular depth of feeling for the natural world and he was attuned to the emotions of animals. Yet it seems that preservation of nature was not on Leonardo's mind.