How did Renaissance composers use folk tunes in masses and motets?

During the Renaissance, composers frequently incorporated secular folk tunes into sacred works like the mass and motet by utilizing them as a cantus firmus—a preexistent melody that served as the structural foundation for a polyphonic composition.12

While the cantus firmus was traditionally derived from liturgical plainchant, Renaissance composers increasingly adopted secular melodies, including popular folk songs and the top lines of French chansons, as source material. In these settings, the chosen melody was typically placed in the tenor voice, often presented in long, sustained notes, while the other voices provided free contrapuntal elaboration.12

A prominent example of this practice is the secular song "L'Homme armé" ("The Armed Man"), which served as the basis for more than 30 different masses by various composers, including Guillaume Dufay, Josquin des Prez, and Giovanni Pierluigi da Palestrina. By integrating these recognizable secular themes into sacred structures, composers achieved a sense of musical unity and technical ingenuity that defined much of the era's polyphonic tradition.13