How did Renaissance composers use a cantus firmus to connect the movements of a mass?

During the Renaissance, composers utilized the cantus firmus technique to provide structural unity across the various movements of a mass. By embedding a pre-existing melody—such as a plainchant excerpt or a secular tune—into the tenor voice of each movement, composers created a consistent musical foundation that linked the entire work together.1

While the cantus firmus was traditionally placed in the tenor, it could also be ornamented or paraphrased in the top voice. Beyond its structural role, the choice of melody often carried symbolic significance. Composers frequently drew from popular secular sources, such as the chanson "L'Homme armé," which served as the unifying cantus firmus for numerous masses by prominent figures like Guillaume Dufay and Josquin des Prez. Additionally, composers could derive a subject from non-melodic sources, such as the solmization syllables extracted from a name, as seen in Josquin’s Missa Hercules Dux Ferrariae.1