How did Giovanni Pierluigi da Palestrina use cantus firmus in his masses?

Giovanni Pierluigi da Palestrina utilized the cantus firmus—a preexistent melody—as a foundational technique in several of his masses. In these works, he typically employed the cantus firmus in the tenor voice part.1

Examples of masses where Palestrina used this technique include Ecce sacerdos magnus, L’Homme armé, Ut, re, mi, fa, sol, la, Ave Maria, Tu es Petrus, and Veni Creator Spiritus. The titles of these compositions often indicate the source of the specific melody used.1

Beyond simply placing the melody in the tenor, Palestrina demonstrated great contrapuntal ingenuity by ornamenting and decorating solemn plainchants. This allowed him to integrate the cantus firmus seamlessly into the musical texture, sometimes making it nearly indistinguishable from the other freely composed parts of the mass. While he was a master of this time-honored technique, it is important to note that he also utilized other methods, such as the parody technique and free-style composition, throughout his extensive body of work.1