Tomb of Antipope John XXIII

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. According to Ferdinand Gregorovius, the tomb is "at once the sepulchre of the Great Schism in the church and the last Papal tomb which is outside Rome itself".

Cossa had a long history of cooperation with Florence, which had viewed him as the legitimate pontiff for a time during the Western Schism. The tomb monument is often interpreted as an attempt to strengthen the legitimacy of Cossa's pontificate by linking him to the spiritually powerful site of the Baptistry. The evocation of papal symbolism on the tomb and the linkage between Cossa and Florence have been interpreted as a snub to Cossa's successor Pope Martin V or vicarious "Medici self-promotion", as such a tomb would have been deemed unacceptable for a Florentine citizen.

The tomb monument's design included figures of the three Virtues in niches, Cossa's family arms, a gilded bronze recumbent effigy laid out above an inscription-bearing sarcophagus supported on corbel brackets, and above it a Madonna and Child in a half-lunette, with a canopy over all. At the time of its completion, the monument was the tallest sculpture in Florence, and one of very few tombs within the Baptistry or the neighboring Duomo. The tomb monument was the first of several collaborations between Donatello and Michelozzo, and the attribution of its various elements to each of them has been debated by art historians, as have the interpretations of its design and iconography.