Benedictine monks who are famed for their Gregorian Chants.

Pope Gregory I the Great is the pope you are referring to. He did not write Gregorian Chants. He compiled and cataloged the plain songs that were used in liturgies at the time. Later they became known as Gregorian Chants.

Gregorian chants are monophonic.

Gergorian chants are no longer written as they were long ago.

Pope St. Gregory I, 'The Great,' and cataloged the Gregorian Chants.

Edmund Gregory Hurley has written:

'Gregorian chant for the teacher, the choir, and the school' -- subject(s): Instruction and study, Chants (Plain, Gregorian, etc.), Gregorian chants