The poem Balsamus et munda cera was the creation of Pope Urban V and is composed entirely in Leonine hexameters. Upon the accession of the Venetian Gabriele Condulmaro as Pope Eugenius IV, however, Dufay began what was to become a succession of large-scale motets that chronicle several events of historical importance in this pope's reign. In October 1428 Guillaume Dufay, then about thirty years of age, entered the service of Pope Martin V as a singer in his papal chapel. Surviving today in a mid-fifteenth-century music manuscript compiled in Trento, Italy, is a SanctusAgnus dei pair ascribed to Dufay. In 1699 the architectural historian Giovanni Ciampini reported that this maze was full of twists and turns, yet was identical in shape to the labyrinth at St. Michael's church in Pavia. Pope Eugenius IV chose the palace of Santa Maria in Trastevere, situated just to the west of the church, as his principal Roman residence.