Exactly 700 years ago this week, on November 18, 1302, Pope Boniface VIII made an extraordinarily bold statement: "Now, therefore, we declare, say, determine and pronounce that for every human creature it is necessary for salvation to be subject to the authority of the Roman pontiff." Even non-human creatures outside the pope's jurisdiction might be in trouble, for the bull in which Boniface's statement appears, Unam Sanctam, also calls up the image of the universal flood:

"Urged by faith, we are obliged to believe and to maintain that the Church is one, holy, catholic, and also apostolic. We believe in her firmly and we confess with simplicity that outside of her there is neither salvation nor the remission of sins . …There had been at the time of the deluge only one ark of Noah, prefiguring the one Church, which ark, having been finished to a single cubit, had only one pilot and guide, i.e., Noah, and we read that, outside of this ark, all that subsisted on the earth was destroyed."

The bull almost sounds like a threat, which would not have been out of character for Boniface. He ascended to the papal throne when his predecessor, Celestine V, abdicated—probably at Boniface's not-so-subtle suggestion. He sentenced the poet Dante to death for alleged financial misdeeds, though Dante escaped by going into exile (and got his revenge by consigning Boniface to the Inferno). When France's King Philip tried to assert autonomy from Rome, Boniface replied, "Our predecessors have deposed these kings of France. Know—we can depose you like a stable boy if it prove necessary."

Despite its tone of finality, though, Unam Sanctam was hardly the papacy's last word on the relationship between Roman Catholicism and other forms of Christianity. ...