Gregorian chant is the central tradition of Western plainchant, a form of monophonic liturgical chant of Western Christianity that accompanied the celebration of Mass and other ritual services. This vast repertory of chants is the oldest music known as it is the first repertory to have been adequately notated in the 10th century. In general, the chants were learnt by the viva voce method, that is by following the given example orally, which took many years of experience in the Schola Cantorum.