Gregorian chant is beautiful and prayerful music.

'Polyphony' does not describe Gregorian chant.

Gregorian chant or Plaint chant is known as monophony. Many voices, unaccompanied, and all singing in unison.

Giovanni Pierluigi da Palestrina diverted the return to Gregorian chant by demonstrating the beauty and reverence of polyphonic music in his compositions. He is credited with saving polyphony from being banned by the Council of Trent and his music became a model for sacred music in the Catholic Church.

monophonic