How do we figure Charlemagne's coronation by the Pope into the equation? Ambiguity still persists, and the consequences were to depend mostly on the future kings to possess the title. On the surface, Pope Leo III had a need for a powerful protector against local Roman rivals as well as petty kings. Charlemagne was the best possibility. As well, the crowning of Europe's most powerful secular ruler by the head of Europe's church symbolized the unity of purpose and destiny between state and religion that had existed in Constantine's Rome, and that had been lamented as passing with the ancient order's demise. As well, Charlemagne was a self-consciously Christian ruler, equating his advance with that of the religion.
There was another, more problematic side to it, however. By placing the crown on the Carolingian's head, the Pope had made symbolic claim to supremacy over the secular. Charlemagne is reported to have thoroughly resented this. Something of a precedent was set; Louis would have himself re-coronated by the Pope after Charlemagne's death, while all inheritors of the Imperial title would hasten across the Alps to Rome to be recognized by the Papacy. Still, given the realities of power, it was most often the Pope who was dependent on Carolingian kings. The powerful ones interfered in Papal elections when possible, and popes in turn made efforts not to cross Imperial desires. Finally, assumption of the Imperial title aggravated Charlemagne's relations with Byzantium for a time.
Historians impressed with the Carolingian achievement have often referred to a cultural 'renaissance' during Charlemagne's rule and that of his son Louis. It is true that he did want to revive something of classical learning, as part of his inheritance of Rome's legacy, and as part of claims to true European/Christian leadership. Learned men in touch with the Latin classical tradition were brought to the palace, conducting something like a school for aspiring elites. These included Alcuin, from the school of York steeped in Irish-English learned traditions; the Italian Peter of Pisa, the grammatical expert, Paul the Deacon, who wrote a Lombard history; as well as Theodulf, a Spaniard trained in Isidore of Seville's traditions. The classical division of knowledge into trivium and quadrivium was ressucitated, and Charlemagne also invigorated monasteries as centers of classical learning's preservation. Here, Hrabanus Maurus and Walafrid Strabo's biblical commentaries would influence medieval Christian thought for centuries. What must be remembered in all of this is that there was absolutely no percolation beyond the walls of the palace or monasteries. Only about a dozen writers were involved, and it was mostly derivative as opposed to creative. The contribution was the preservation of learning for later times, as ensuing civil wars and foreign invasions sapped much of its vigor.
Ultimately, the Carolingian state decayed for the same reasons as did its predecessor. The end of foreign conquest provided fewer opportunities for rulers to exhibit martial prowess and distribute financial largesse. As well, Frankish kings could not let go of the notion that the royal patrimony ought to be split among a ruler's heirs. And, Carolingian successors were never satisfied with their allotments. Added to this was the conjuncture of less skilled kings such as Louis the Pious, or young-dying ones whose lands were divided by other relatives. Through these processes, lands were repeatedly divided along lines roughly parallel to the divisions of France and Germany. By the end of the ninth century, latent cultural differences between Aquitane, Burgundy, and Ile de France (Paris), on the one hand, and Austrasia, Saxony, Bavaria, and other eastern areas on the other, would condition the emergence of separate polities in the next two-and-a-half centuries.