We should start by charting the broad outlines of the place of the medieval church in Western Europe. I should start off by noting that this is a huge topic – as will swiftly become clear, there was almost no part of society in which the Church did not play a significant role – and I will only be offering a broad-strokes overview here, sufficient to provide a basis of comparison for [Game of Thrones]. Most of this discussion will principally concern the Latin Church (what today is the Catholic Church) in the West. Since this discussion is – importantly! – about the state of affairs before the reformation, I will tend to refer to the Latin Church simply as “the Church” for brevity’s sake.

The very first thing to note is that the Church (in this case, both the Latin West and the Greek East) pre-dated the Middle Ages themselves. The Church arrived in the Middle Ages as relic of the Roman Imperial past. It inherited Roman Imperial organization – the diocese, for instance, derived from the boundaries of Roman super-provinces called dioceses (Greek: διοίκησις). Unlike the new medieval aristocracy, which tended to rule from fortified estates in the countryside, the Church remained centered in towns and cities, many of which had been major centers under the Romans. As the Roman provincial administration collapsed, it largely fell to the Church – as one of the few surviving literate institutions – to replace some of the core functions, like record keeping and the preservation of literature and learning. This was less true [in] Scandinavia and Eastern Europe, places where the Church was a relative late-comer, but for most of Western Europe, the Church was not some new institution grafted on to a pre-existing society (as it had been under the Romans), but rather part of the bedrock cultural foundation upon which that new society was constructed (fellow pedants! – please note carefully the phrase part of in the previous sentence; I am aware there were other things).

That said, the institutional power of the Church (and here we really do mean what would be the Roman Catholic Church) begins to change dramatically in the 11th century, right as we enter the High Middle Ages, and continues for the next several centuries (keeping in mind that Game of Thrones and A Song of Ice and Fire really evoke the High and Late Middle Ages, rather than the Early period). In short, the institutional heft of the Church grows dramatically. Quite a few things begin happening which are linked together: the Popes begin trying to wrest control over the Church’s hierarchy (specifically, the investiture of bishops) from secular rulers. Clerical celibacy was more stringently enforced. The Church intruded into warfare (as we’ve discussed with the Peace of God / Truce of God movements). It began to more directly attempt to regulate marriage, especially among the powerful (marriage was a made a sacrament in 1184). By the 1300s, this included keeping detailed records in many parts of France about births, deaths and marriages, in part to ensure no one married a close relative.

(And, of course, for those of you thinking, “wait, isn’t this also the period of the Crusades – military expeditions called by and at least nominally (but not in practice) under the auspices of the Pope?” Yes, it is, and that’s not an accident either).

In my experience teaching this, it is the next step that baffles my students the most. This vast increase in the institutional power of the Church was made possible, not by armies or shrewd real-politic (though both were involved), but by belief. The primary weapon wielded by Popes in this effort was the threat of excommunication, which (under Catholic doctrine) cut off the excommunicated individual or community from salvation, potentially damning them for all eternity. But of course that threat is only real if you believe the Pope has that power. And therein is the key point: most of Europe did believe. As I tell my students, it is safe to assume, as a general matter, that people in the past believed their own religion. Of course there are exceptions, but the general rule remains.

In the conflicts that arose – because, as you might imagine, secular rulers were unwilling to give up their prerogatives – it did not actually much matter if the king or emperor believed in the power of excommunication, because no one rules alone. Thus when the Holy Roman Emperor Henry IV was excommunicated by Pope Gregory VII in 1076, the audience for this act wasn’t Henry himself (who had already declared Gregory illegitimate anyway). It was directed at all of Henry’s vassals and supporters, releasing them from their oaths of allegiance and essentially saying, “stick with this guy, and he’ll take you to hell with him”. It worked, sparking a major rebellion and forcing Henry to humiliatingly apologize the following year.

(History note: this would be “round 1” in a multi-round fight that wasn’t settled until 1122 with the Concordat of Worms; in the end the Papacy mostly won, sharply limiting the Holy Roman Emperors’ power over their bishops).

Bret Devereaux, “New Acquisitions: How It Wasn’t: Game of Thrones and the Middle Ages, Part II”, A Collection of Unmitigated Pedantry, 2019-06-04.