Fascinating and very readable. Charts the development, not only of the papacy, but of Western civilization itself (at least in the year of our Lord).
While O'Malley does occasionally try to find evidence for the Roman bishop's predominant leadership role in the earliest years of the church, he seems perfectly aware that the reality, or at least what we have to go off of, is much more ambiguous. He admits that most old lists begin with Linus - not Peter. He points out that, before the title "pope" was given solely to Rome's bishop, it had been used for all other bishops, as was the title "vicar of Christ" (before Innocent III, Roman bishops had sometimes been referred to as the "vicar of Peter"). He never really explains why the bishop of Milan excommunicated the Roman emperor (and that during the papacy of Damasus, who insisted on the preeminence of the "Apostolic See", and referred to fellow bishops as "sons", to the consternation of the Eastern bishops).
O'Malley, as might be expected, highlights how tied up the popes had been in the political affairs of Europe. This, of course, is seen in the coronation of Charlemagne, the Donation of Pepin, etc., but also in the remarkable encounter between Leo the Great and Attila the Hun (which somehow or another resulted in Attila's backing off).
So O'Malley tells the story of an office that from its earliest days enjoys a special kind of respect and prestige (maybe nostalgic?) but grows (almost always at the insistence of the office-holder, but also the unchecked loyalty of others [I wonder if some of that loyalty doesn't stem from some kind of patriotism: East vs. West, etc.]) into the kind of authority that would claim infallibility and determine dogma unilaterally.
Enjoyable and informative. I suggest reading it.