Three of Michelangelo's letters on the subject to the Duke have been preserved.

After giving a short history of the project, and alluding to the fact that Leo X.began the church, he says that the Florentines had appointed a building committee of five men, at whose request he made several designs.

One of these they selected, and according to his own opinion it was the best.

"This I will have copied and drawn out more clearly than I have been able to do it, on account of old age, and will send it to your Most Illustrious Lordship." The drawings were executed and carried to Florence by the hand of Tiberio Calcagni.

Vasari, who has given a long account of this design, says that Calcagni not only drew the plans, but that he also completed a clay model of the whole church within the space of two days, from which the Florentines caused a larger wooden model to be constructed.