Priests of the Vedic religion are officiants of the yajna service. As persons trained for the ritual and proficient in its practice, they were called ("regularly-sacrificing"). As members of a social class, they were generically known as vipra "sage" or kavi "seer". Specialization of roles attended the elaboration and development of the ritual corpus over time. Eventually a full complement of sixteen s became the custom for major ceremonies. The sixteen consisted of four chief priests and their assistants.