Plainsong is a type of CHANT, specifically a form of monophonic, unaccompanied sacred song of the Christian Church. It is also known as Gregorian CHANT, named after Pope Gregory I, who is traditionally credited with its invention. Plainsong is sung by a single voice or unison choir without any instrumental accompaniment. It is characterized by its simple and repetitive melodies, which are often based on a single repeated phrase.