This term refers to an unbroken chain of the spiritual authority of Church leaders that originated with the Apostles and continues to the present-day patriarch. It was used as an argument against Gnosticism from the second century onward.
Hegesippus, in his memoirs against the Gnostics, mentioned for the first time the word diadoche, which could mean either a succession from the Apostles or “continuing to receive from hand to hand” (tradition).
Irenaeus of Lyons, one of the most important theologians of the second century, presented an extensive treatment of the Apostolic Tradition and succession in his book against heresies.
In the Coptic Church, the patriarch is considered to be the successor of St. Mark (who was not among the 12 disciples); in several hymns welcoming the patriarch, the “Successor of St. Mark” is mentioned.