The important contribution of Heinrich Isaac (ca. 1455-1517) to polyphonic settings of the proper of the mass has long been recognised. The monumental posthumously published collection of his
work in the genre, the Choralis Constantinus, was considered as a landmark even in the sixteenth century. Isaac's striking cultivation of polyphonic mass proper settings has its roots in his
task, as Hofcomponist to Emperor Maximilian I, of building a musical repertoire for the Imperial court chapel. The repertoire he created awakened a demand for analogous music at other European
courts and institutions and led, in 1508, to the commissioning of an extraordinary series of proper cycles from him by the authorities of Constance Cathedral.
