We count over forty mass settings using the L’homme armé tune as a cantus firmus in the tenor. The tune about the armed man that is to be feared can be traced back to the mid-15th century political setting of a westward-expanding Ottoman Empire, and the newly founded Order of the Golden Fleece calling for a new crusade, which never materialized. As a mass setting, L’homme armé took on a dynamic of its own and became a composer’s challenge of sorts—from Du Fay, Ockeghem, and Regis to Josquin, Busnois, La Rue, Orto, and Compère, all the great composers of the time are represented with their own setting, displaying their compositional and notational virtuosity. The tenor appears in augmentation, in diminution, in retrograde, in inversion, in fuga (modern canon), in various transpositions, in mensuration canons, and the full range of the possibilities of late 15th century mensural notation is explored.