<P> The earliest musical settings of the Mass are Gregorian chant . The different portions of the Ordinary came into the liturgy at different times, with the Kyrie probably being first (perhaps as early as the 7th century) and the Credo being last (it did not become part of the Roman mass until 1014). </P> <P> In the early 14th century, composers began writing polyphonic versions of the sections of the Ordinary . The reason for this surge in interest is not known, but it has been suggested that there was a shortage of new music since composers were increasingly attracted to secular music, and overall interest in writing sacred music had entered a period of decline . The non-changing part of the mass, the Ordinary, then would have music which was available for performance all the time . </P> <P> Two manuscripts from the 14th century, the Ivrea Codex and the Apt Codex, are the primary sources for polyphonic settings of the Ordinary . Stylistically these settings are similar to both motets and secular music of the time, with a three - voice texture dominated by the highest part . Most of this music was written or assembled at the papal court at Avignon . </P> <P> Several anonymous complete masses from the 14th century survive, including the Tournai Mass; however, discrepancies in style indicate that the movements of these masses were written by several composers and later compiled by scribes into a single set . The first complete Mass we know of whose composer can be identified was the Messe de Nostre Dame (Mass of Our Lady) by Guillaume de Machaut in the 14th century . </P>

What is the first known polyphonic setting of all the sung movements of the mass ordinary