Gregorian Chant , a method of singing the psalms and litanies of the church, introduced by Pope Gregory the Great about 590., It was mainly founded on the Ambrosian chant, previously in use in the western churches, to the four authentic or principal modes of which Gregory, either for variety or convenience of the voice, added the plagal or collateral modes. His additional object in effecting this reform was to banish from the church all rhythmic singing, as too lively for the place and occasion, and to substitute in his own chant, which was called the canto fermo, a gravity and simplicity suited to the solemn offices of the church. He also established in Rome a school of instruction in the new method of singing, which existed for three centuries after his death. Notwithstanding the monotony of the Gregorian chant, its extreme simplicity and dissimilarity to secular music, or even to that at present employed in the services of the church, it is still in use, and during Lent and on other special occasions may be heard in all its ancient glory in Roman Catholic churches, and to a limited extent in those of other denominations.

It has been supposed that fragments of the melodies sung in the celebration of the Eleusinian mysteries are discernible in the Gregorian chant.