What is apostolic succession, and why does the pope claim Peter's line?

Apostolic succession is the idea that the ministry of the Church comes down from the apostles through an unbroken series of bishops. The Roman Catholic and Eastern Orthodox traditions, among others, maintain that a bishop's orders are neither regular nor valid without it. For the pope, the link runs through Peter. The See of Rome claims the full authority of Peter, who according to Catholic doctrine was the visible head of the church, exclusively for itself, because Peter died as the Bishop of Rome and not of another see. Roman Catholicism acknowledges that the papacy is built on apostolic succession, not the other way around.

The idea took shape in the second century. The Anglican bishop Michael Ramsey describes it as originally a response to Gnostic claims of having received secret teaching from Christ or the apostles. The answer was public: the apostles had passed on authentic teaching to those they entrusted with the churches they founded, and these had passed it on in turn. Hegesippus and Irenaeus, around 180, produced succession lists to back this up. Irenaeus's list in Against Heresies runs from Saint Peter to Pope Eleutherius, who served from 174 to 189.

The challenge could be blunt. Tertullian, writing a little later, told rival teachers to "unfold the roll of their bishops, running down in due succession from the beginning". And the lists were never perfectly tidy: Augustine wrote his own list of 38 popes from Peter to Siricius, and its order differs from the list of Irenaeus.

Other traditions tell the story differently. The Ecumenical Patriarchate of Constantinople states that the apostle Andrew was its founder. Strict Eastern Orthodox theology holds that all legitimate bishops are properly successors of Peter. And some Christians, including many Protestants, deny the need for this kind of continuity and severely question the historical claims involved.