The polyptych is Martini's largest work. The altarpiece consists of seven elements, each one in three parts: a cusp, a smaller panel divided into two sections, and a larger panel depicting a single saint. There is also a predella consisting of seven smaller size panels. There are 15 predella figures, an upper row with other 14 figures and seven cusps with other characters. There is a total of 44 busts of apostles, martyrs, bishops and prophets.

The central panel depicts the Madonna with Child; the remaining six main panels are, from left to right, St. Domingo de Guzmán, St. Juan el Evangelista, María Magdalena, St. Catalina de Alejandría, Juan el Bautista and St. Pedro de Verona. Above the Madonna are two archangels Arcángel Gabriel and Arcángel Miguel and, above them, the Christ blessing.

The six saints panel are surmounted by the Twelve Apostles arranged in couples. Each one is carrying a copy of the Gospel and is named on the background. From left to right, Thaddaeus, Simon, Philip and James the Less, talking animatedly about the Scriptures, Andrew and Peter. On the right side of the archangels are Paul and James Major (with a shell in relief between the letters of his name), Matthew writing his Gospel, resting the book on the frame of the panel, Bartholomew, Thomas and Mathias. St. John the Evangelist is replaced by St. Paul.

In the cusps, next to the Blessing Christ, are David playing the harp, Moisés with the Tables of the Law and the prophets Jeremiah, Isaiah, Daniel and Ezechiel. enwp