Leaf from a Gradual: Initial (M) with St. Andrew (recto), c. 1480. This leaf was excised from a volume of a large set of choral books known to have been commissioned by Bartolomeo delle Rovere for Ferrara Cathedral. Delle Rovere, nephew of Pope Sixtus IV, was the Bishop of Ferrara from 1474 to 1494 and his arms appear in the rondel at the bottom of the page-a shield bearing an oak tree ( rovere in Italian) surmounted by a patriarchal cross, the symbol of his rank and authority. Payment records indicate that Argenta worked on the choir books for Ferrara Cathedral from 1478 to 1486. The initial M introduces the chant for the Introit (introduction) to the mass for the Feast of Saint Andrew, celebrated on November 30. This date also marks the beginning of the Advent season (leading to Christmas) in the liturgical calendar.