The Tomb of Antipope John XXIII is the marble-and-bronze tomb monument of Antipope John XXIII (Baldassare Cossa, c. 1360–1419), created by Donatello and Michelozzo for the Florence Baptistry adjacent to the Duomo. It was commissioned by the executors of Cossa's will after his death on December 22, 1419 and completed during the 1420s, establishing it as one of the early landmarks of Renaissance Florence.