For the same Rucellai Leon Batista made a chapel in the same manner in S. Pancrazio, which rests on great architraves placed on two columns and two pilasters, piercing the wall of the church below; which is a difficult thing, but safe; wherefore this work is one of the best that this architect ever made. In the middle of this chapel is a tomb of marble, wrought very well in the form of a rather long oval, and similar, as may be read on it, to the Sepulchre of Jesus Christ in Jerusalem.
About the same time Lodovico Gonzaga, Marquis of Mantua, wished to build the tribune and the principal chapel in the Nunziata, the Church of the Servi in Florence, after the design and model of Leon Batista; and pulling down a square chapel, old, not very large, and painted in the ancient manner, which stood at the head of the church, he built the said tribune in the bizarre and difficult form of a round temple surrounded by nine chapels, all curving in a round arch, and each within in the shape of a niche. Now, since the arches of the said chapels rest on the pilasters in front, the result is that the stone dressings of the arches, inclining towards the wall, tend to draw ever backwards in order to meet the said wall, which turns in the opposite direction according to the shape of the tribune; wherefore, when the said arches of the chapels are looked at from the side, it appears that they are falling backwards, and that they are clumsy, as indeed they are, although the proportions are correct, and the difficulties of the method must be remembered. Truly it would have been better if Leon Batista had avoided this method, for, although there is some credit for the difficulty of its execution, it is clumsy both in great things and in small, and it cannot have a good result. And that this is true of great things is proved by the great arch in front, which forms the entrance to the said tribune; for, although it is very beautiful on the outer side, on the inner side, where it has to follow the curve of the chapel, which is round, it appears to be falling backwards and to be extremely clumsy. This Leon Batista would perhaps not have done, if, in addition to science and theory, he had possessed practical experience in working; for another man would have avoided this difficulty, and would have rather aimed at grace and greater beauty for the edifice. The whole work is otherwise in itself very beautiful, bizarre, and difficult; and nothing save great courage could have enabled Leon Batista to vault that tribune in those times in the manner that he did. Being then summoned by the same Marquis Lodovico to Mantua, Leon Batista made for him the models of the Church of S. Andrea and of some other works; and on the road leading from Mantua to Padua there may be seen certain temples built after his manner. Many of the designs and models of Leon Batista were carried into execution by Salvestro Fancelli, a passing good architect and sculptor of Florence, who, according to the desire of the said Leon Batista, executed with judgment and extraordinary diligence all the works that he undertook in Florence. For those in Mantua he employed one Luca, a Florentine, who, living ever afterwards in that city and dying there, left his name--so Filarete tells us--to the family of the Luchi, which is still there to-day. It was no small good-fortune for him to have friends who understood him and were able and willing to serve him, because architects cannot be always standing over their work, and it is of the greatest use to them to have a faithful and loving assistant; and if any man ever knew it, I know it very well by long experience.