In an earlier post, I discussed how early medieval popes had an abstract moral authority, considered the heirs of Saint Peter, even while most people didn't even know who the pope was, and a lot of the men who became pope were far from holy. They certainly weren't telling Christians what to believe.
A sign of the relative weakness of the popes is the ninth-century Pseudo Isidorian Decretals, so called because they claimed (falsely) to be written by the somewhat earlier legal scholar Isidore of Seville. These Decretals were written to make it easier for bishops to avoid being judged by their fellow-bishops if they had done something wrong. They claimed that bishops could be judged only by the pope, which meant, in practice, that they couldn't be judged at all!
In addition, the popes, until the eleventh century, continued writing their letters on papyrus, which had been the formal material for letters since the Roman Empire. Because they only had a limited amount (once Egypt, where papyrus came from, was in Muslim hands), they didn't write many letters. They also continued to use the handwriting of the late Empire, almost incomprehensible in the West, which had, since around 800, used a form of writing that looks a lot like modern printing.
The papacy suddenly emerged into European politics in the 1040s. The German king went to Rome to be crowned Roman emperor, as German kings had been doing for over two centuries. He was shocked to discover three different men fighting in the streets over who should be pope. He assembled a council of the churchmen who had accompanied him, declared all three popes deposed, and had one of his men elected pope instead. Crowned emperor, he happily headed home. "My work here is done."
The first and second German popes quickly died, probably poisoned. The third German pope, Leo IX (1049-1054), originally from Alsace, had the good sense to get out of Rome. He moved around western Europe holding councils. He was trying to improve the overall morality of the church, primarily by making sure all bishops were good, moral and well-educated men who had properly been elected, not buying their office or seizing it by force.
The bishops took this surprisingly well. The Pseudo-Isidorian Decretals, believed at the time to be the true decisions of councils of the earliest days of the Church, helped a lot. By saying that bishops could be judged by popes, it gave the popes a real authority they had not previously had.
The emperors did not forget that they had been responsible for reforming the popes. A generation later, in the 1070s, pope and emperor got involved in a knock-down, drag-out battle now called the Investiture Controversy. This is because the initial discord was over the question of who could "invest" a newly-elected bishop with the symbols of his office (ring and pastoral staff). The German emperors had always done so and weren't interested in popes who told them this was inappropriate. The quarrel quickly became a contest over who was the ultimate authority in a Christian empire, pope or emperor. It dragged on for two generations, both sides declaring the other a heretic, or declaring the other deposed, or announcing they were going to follow a different pope or a different emperor.
So, we're now up to 1130, and we've yet to see popes having real authority. Stay tuned.