As early as 1442 Pope Martin V had given the Medicis permission to build a private chapel with a portable family altar. The chapel, in the first floor of the Medicis' private residence, was built by Michelozzo di Bartolomeo between 1446 and 1449 and dedicated to the Holy Trinity. It comprises an almost square main room and, one step higher, an equally nearly square chancel. The two are separated from each other by two Corinthian pillars. Cosimo de' Medici chose Benozzo Gozzoli to decorate the chapel, and this commission brought the artist back to Florence. The pictorial program of the chapel is also structured in two parts: the Procession of the Magi in the main room and the Adoration of the Child in the chancel with the Angels worshipping on the side walls. The ceiling is decorated by a diamond-pointed ring in a halo with a loop that bears the motto of Piero de' Medici, semper, and within it inside a glory the monogram of Christ, JHS, as used for St Bernardino of Siena. The Procession of the Magi extends across the east, south and west walls of the main room above the encircling benches. These three walls were painted in about 150 working days, and each represents one of the Three Kings. (The names of the kings are Caspar, Melchior, Balthazar, however, we do not use them because they are frequently confused in various sources.) This is a result of the allocation of the abbreviation of their names, CMB.The east wall leads off with the youngest king, the story continues on the south wall with the middle king, and ends on the west wall with the oldest king. An unusual feature of this depiction is that the procession does not arrive at the manger. The adoration of the Christ Child was reserved for the contemporary observers present in the room, and their prayers were said within the important framework of the procession of the magi taking place on either side. The Procession of the Magi moves towards Filippo Lippi's altar painting of the Adoration of the Child. The original, which was replaced with a copy in 1494, is now in the Staatliche Museen in Berlin. The copy is attributed to the pseudo-Pier Francesco Fiorentino. However, the altar painting does not just depict the Adoration, it also shows the Holy Trinity God the Father, the Holy Spirit and Christ are united on the painting and represent the conception of the Holy Trinity held by the Western Church: the Holy Spirit emanates from the Father and Son. This contrasts with the view held by the Orthodox Church, in which the Holy Spirit emanates from God the Father alone. The picture reflects the debate on general principles that took place between the Orthodox and Western Churches at the Council of Ferrara-Florence in 1439. In the apse the ranks of angels, with marvelously ornate clothes and wings, are depicted in the act of flying, singing, worshipping on their knees, and weaving festoons of flowers; the verses inscribed in their haloes tell us that the hymn they are intoning is the Gloria. Having begun the work in the spring-summer of 1459, Benozzo completed the work rapidly over the space of a few months, with the help of at least one assistant (probably Giovanni di Mugello), under the supervision of Piero di Cosimo de' Medici or his friend and confidant Roberto Martelli. It was probably Piero de' Medici who suggested that the artist should use Gentile da Fabriano's Adoration of the Magi as a model for the frescoes. The extraordinary complexity and subtlety of the technique of execution, in which true fresco alternated with dry fresco, permitted the painter to work with meticulous care, almost as if he was engraving, like the goldsmith he had been in Ghiberti's workshop, not just the precious materials of jewelry, fabrics, and harnesses, but even the trees laden with fruit, the meadows spangled with flowers, the variegated plumage of the birds, and the multicolored wings of the angels. Finally, leaves of pure gold were applied generously to shine in the dark, in the dim light of the candles.