Since the 16th century “Cardinal” has been an exclusive designation for the members of the College of Cardinals, also called the Sacrum Collegium, which consists of three classes (cardinal bishops, cardinal priests, and cardinal deacons).

1. History. The historical roots of the College of Cardinals go back to the presbyterate of the Bishops of Rome. According to an old custom, which held fast to the memory of the eucharistic celebration by the bishop together with his presbyterate, the heads of the Roman titular churches, whose nu…