Missa Papae Marcelli  Missa Papae Marcelli, or Pope Marcellus Mass, is a mass "sine nomine" by Giovanni Pierluigi da Palestrina. It is his best-known mass, and is frequently taught in university courses on music. It was sung at the Papal Coronation Masses (the last being the coronation of Paul VI in 1963). The "Missa Papae Marcelli" consists, like most Renaissance masses, of a Kyrie, Gloria, Credo, Sanctus/Benedictus, and Agnus Dei, though the third part of the Agnus Dei is a separate movement (designated "Agnus II"). The mass is freely composed, not based upon a cantus firmus or parody. Perhaps because of this, the mass is not as thematically consistent as Palestrina's masses based on models. It is primarily a six-voice mass, but voice combinations are varied throughout the piece; Palestrina scores Agnus II for seven voices, and the use of the full forces is reserved for specific climactic portions in the text. It is set primarily in a homorhythmic, declamatory style, with little overlapping of text and a general preference for block chords such that the text can clearly be heard in performance, unlike many polyphonic masses of the 16th century. As in much of Palestrina's contrapuntal work, voices move primarily in stepwise motion, and the voice leading strictly follows the rules of the diatonic modes codified by theorist Gioseffo Zarlino. The mass was composed in honor of Pope Marcellus II, who reigned for three weeks in 1555. Recent scholarship suggests the most likely date of composition is 1562, when it was copied into a manuscript at the Basilica di Santa Maria Maggiore in Rome. The third and closing sessions of the Council of Trent were held in 1562–63, at which the use of polyphonic music in the Catholic Church was discussed. Concerns were raised over two problems: first, the use of music that was objectionable, such as secular songs provided with religious lyrics (contrafacta) or masses based on songs with lyrics about drinking or lovemaking; and second, whether imitation in polyphonic music obscured the words of the mass, interfering with the listener's devotion. Some debate occurred over whether polyphony should be banned outright in worship, and some of the auxiliary publications by attendants of the Council caution against both of these problems.