(cantus) is used for the vocal music of churches. In church history we meet with divers kinds of chants or songs. The first is the Ambrosian, established by St Ambrose; the second is the Gregorian, introduced by Pope Gregory the Great, who established schools of chanters, and corrected the church song. This is still retained in the church under the name of plain song; at first it was called the Roman song. The plain or Gregorian chant is where the choir and people sing in unison, or all together in the same manner.