Leonardo da Vinci began painting the Mona Lisa in 1503. The date is supported by an October 1503 marginal note by Agostino Vespucci, who wrote that Leonardo was working on a portrait of Lisa del Giocondo.
The exact chronology is more complicated than the quiz answer suggests. The Louvre generally dates the painting to 1503–1506, but Leonardo may have continued refining it for years. Some historians argue that work continued until around 1516 or 1517, after Leonardo moved to France at the invitation of King Francis I.
A common mistake is choosing 1519, the year Leonardo died. That is not the starting date; it is the year associated with the end of his life and the painting’s transfer into the French royal collection. The 1503 date identifies when work on the portrait began.