Completion
The chronology of the tomb monument's completion is not precisely known, but portions can be determined from various sources. According to the passing reference of a Florentine notary, in 1424 (by the Florentine calendar) part of the tomb was installed. Michelozzo's Catasto from July 1427 indicates that Michelozzo had been Donatello's partner for about two years ("due anni o incircha") and that three-fourths of the 800 florin budget had been spent. To harmonize these accounts, one must conclude either that Michelozzo's chronology was imprecise, that Donatello received the commission before the partnership was formed, or that the 1424 date in the Florentine calendar falls in 1425 in the modern calendar.
On February 2, 1425, Bartolomeo Valori and Cosimo de' Medici requested 400 of the 800 florins that had been deposited with the Calimala, likely for work already completed. This deposit was insurance in case the executors left the tomb unfinished and the Calimala was forced to pay for its completion, as it had been obliged to with the finger reliquary. This request is also the most direct piece of evidence for Cosimo's involvement with the commissioning. Despite this document, Vasari's claim in his Vite of 1550 that Cosimo was responsible for the handling of the commission has been questioned.
It is probable that the sarcophagus was installed on or shortly before May 2, 1426, when the Calimala contracted for two chaplains to say a daily mass for Cossa's soul. The records of the Duomo workshop indicate that on January 28, 1427 Valori bought four white marble blocks for the tomb.
The exact date of completion is unknown but an extreme terminus ante quem is given by the death in 1431 of Pope Martin V, who is known to have visited the completed tomb; other factors may push the terminus ante quem back significantly into the 1420s. The most reliable such indication is that in September 1428 Jacopo della Quercia returned to Bologna and produced a wall tomb with Virtues reflecting in minute details the Cossa Virtues.
Vasari suggests that the tomb went over budget, costing 1,000 florins, although it is unclear who covered the excess. Although the original source for this claim is unknown, it has gained credence with modern scholars as the effigy alone would have cost 500 florins, yet its exactness may be taken with a grain of salt.
Read more about this topic: Tomb Of Antipope John XXIII