Palestrina wrote over 100 masses for various combinations of voices. Of these masses, around 50 are adaptations based on previously composed music by Palestrina himself or others before him. Many of the rest are based on plainchant which provides the melodic material. Of these chant-based works, 30 are considered "paraphrase masses" in which the chant is not confined to just the tenor voice but fragments of the line are passed throughout all the voices. Alternate parts have been provided for several voices.