"I don't believe Peter was ever Bishop in Rome," he deliberated, quite early on.
Scholars are apparently still uncertain why Paul, who seemed to make the bigger effort to extend the Word to gentiles, was downgraded relative to Simon Peter once Christianity became the state religion in Rome. Perhaps it was simply that Greek pun — "upon this rock" — put into Jesus' mouth that earned Peter a basilica downtown, while Paul's church and final resting place was stuck outside the city walls.
The Abbot of said church was admirably frank in expressing a hope that the legacy of 'his' saint should achieve greater influence in modern Catholicism, and observing that if Paul not Peter had become the gatekeeper, the church would have had a much less centralised look about it today.
MacCulloch himself betrays a slight Anglican bias on these matters. For he categorically blames St Augustine of Hippo for all of western Christianity's sexual complexes (and specifically of course the doctrine of original sin) whilst failing to note that it was Paul who was the monster misogynist.
In the Dark Ages old controversies still complicated the religious scene — such as the Arianism espoused by the Goths. So the papacy made the decision to outflank this encroaching heresy by converting the Anglo-Saxons in the late sixth century and establishing a particularly loyal bond between these gauche northerners and the Bishop of Rome.
For his services Augustine , the leading Benedictine missionary in England and special papal envoy, was presented with the See of Canterbury and a pallium, which still features in the Anglican Archbishop's coat of arms a half a millennium after the English Reformation.
With no Emperor in Rome at this time, the Italian aristocracy entered the priesthood in droves (The Catholic Bishop's get-up today reflects the secular garb of Rome's fufurufos at this time.) and local secular power was increasingly concentrated in the person of the Pope.
The Papacy was helped first by the eradication of three out of four rival patriarchs (Antioch, Alexandria and Jerusalem) by Jihad and by the forged Imperial decree known as The Donation of Constantine (not in fact mentioned on the programme) which supposedly transfered control of the western half of the empire to the Pope in the absence of any other capo in the region.
On Christmas Day 800 Pope Leo III felt secure enough to share some of this ascendency by crowning the biggest barbarian then knocking around — Charlemagne — as the first 'Holy Roman Emperor.'
But a Papacy controlled by wealthy Roman toffs was hardly a model Christian institution. A zeal for change soon arrived in the person of the brutish reformer Gregory VII, whose main achievements might be said to have been:
1) Getting himself embroiled in a war with the very institution that Leo III had created, which destablised Europe (and Germany in particular) for centuries and perhaps could be said to have ultimately resulted in two World Wars thanks to Rome's continued efforts to stifle German nationalism and centralised leadership from this point onwards. (MacCulloch didn't actually say this though!)
2) Getting rid of married priests, largely in order to counteract the laws of inheritance that prevailed amongst the aristocracy and thereby establish the Pope's unchallenged authority in the selection process for the key ecclesiastical posts. (Up until this point only 'regular clergy' i.e. monks and nuns were expected to be celibate.)
3) Getting the ideological wheels moving which would lead to exciting new doctrines on the remission of sin, which would pave the way for the Crusades and the sale of indulgences which would in turn eventually culminate in the Reformation and part four (?) of this very interesting programme.
Part 3 meanwhile will cover the 'Orthodox' church. Gregory had been helped by the actions of his predecessor Leo IX who had got shot of Constantinople and both its Emperor and its Patriarch, the last serious rivals to the Pope's claim to head up "all Christendom". This was achieved by sending Rome's least tactful legate Humbert for a crucial meeting with Patriarch Michael in 1054 which concluded with a frenzy of mutual excommunications.