In the history of Christianity, "Pentarchy" (from the Greek Πενταρχία, Pentarchia from πέντε pente, "five", and ἄρχω archo, "to rule") is a proposed organisational structure where Christendom is ruled by the heads (or Patriarchs) of the five major episcopal sees of the Roman Empire: Rome, Constantinople, Alexandria, Antioch, and Jerusalem.