Missa Papae Marcelli, or Pope Marcellus Mass, is Palestrina's most well-known and most often-performed mass, and is frequently taught in university courses on music. The mass is freely composed, not based upon a cantus firmus or parody. It is a six-voice mass, though the use of the full forces is reserved for specific climactic portions in the text, and voice combinations are varied throughout the piece. 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, unlike many polyphonic masses of the 16th century, can clearly be heard in performance.