Michelangelo and Leonardo lived five centuries ago, but their works still obsess our culture, with a popular and universal quality that nothing else matches. They have been equally revered and famous since their lifetimes, but our admiration for them exists mostly in isolation of each other. But in 1504 they competed with each other directly, to paint the walls of a room in Florence's Palazzo Vecchio. It is remarkable enough that the same city had produced two such geniuses in the same century -- let alone that they met and exhibited together. But this competition, perhaps the most important event in the history of Renaissance art, the moment at which individual style came to command its own value, has been largely forgotten because the rival works did not survive.