Of Leonardo da Vinci's works, the Mona Lisa is the only portrait whose authenticity has never been seriously questioned, and one of four works – the others being Saint Jerome in the Wilderness, Adoration of the Magi and The Last Supper – whose attribution has avoided controversy. He had begun working on a portrait of Lisa del Giocondo, the model of the Mona Lisa, by October 1503. It is believed by some that the Mona Lisa was begun in 1503 or 1504 in Florence.
