Bishops in all of these communions are ordained by other bishops through the laying on of hands. While traditional teaching maintains that any bishop with apostolic succession can validly perform the ordination of another bishop, some churches require two or three bishops participate, either to ensure sacramental validity or to conform with church law. Catholic doctrine holds that one bishop can validly ordain another (priest) as a bishop. Though a minimum of three bishops participating is desirable (there are usually several more) in order to demonstrate collegiality, canonically only one bishop is necessary. The practice of only one bishop ordaining was normal in countries where the Church was persecuted under Communist rule.