During the brilliant age that produced a Machiavelli and an Erasmus, Heinrich Isaac became one of the recognized masters of secular as well as religious music. Before his death in 1517 he had served both Lorenzo the Magnificent in Florence and Emperor Maximilian I in Vienna and Augsburg. His Choralis Constantinus ranks with Johann Sebastian Bach's Art of the Fugue as one of the epochal works in the history of music. But it is only with the publication of these Five Polyphonic Masses that the entire Formschneider first edition (Nürnberg, 1555) is at last made available to modern scholars and musicians. Unquestionably the most serious and most significant of Isaac's varied and numerous works are his Masses. Among his finest and most characteristic are these five magnificent settings for the Ordinary of the Mass, which appear at the close of Part III of the Choralis. In the present modern notation, after three centuries, they again take their place as music to be performed.