Viderunt omnes

Gregorian chant

"Viderunt omnes" is a Gregorian chant based on Psalm XCVIII (98), sung as the gradual at the Masses of Christmas Day and historically on its octave, the Feast of the Circumcision. Two of the many settings of the text are famous as being among the earliest pieces of polyphony by known composers, Léonin and Pérotin of the Notre Dame school. Their music, known as organum, adds florid counterpoint to the Gregorian melody of the intonation and verse, portions normally sung by the cantors, the remainder of the chant being sung unchanged by the choir.

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