To fully understand how the "Holy Roman Empire" came into existence, we have to go back to the year 800 Christmas day, when Pope Leo III coronated Charlemagne in Rome. The Roman empire prior had been continued by the Eastern Roman Empire, and this is the important distinction. To those in the Eastern Roman Empire, and many other places in Europe and the known world, the Roman Empire had never ceased to exist, so there was not a succession but rather a continuation of it. This distinction is important as we take a look at the year 797.

During the year 797, Irene of Athens had outmanuevered her son Constantine VI and had his eyes gouged out, leading to his death. While she had initially been her son's regent, and then co-regent with him once he had matured, this event left her as the sole leader of the Eastern Roman Empire, and as such she assumed the title of "Empress".

Now prior to this, the Holy See of Rome had been a sort of 'protectorate' of the Eastern Roman Empire, though this gradually declined until the mid-700s, with Pope Gregory III excommunicating the Eastern Roman Empire due to Iconoclasm, and Pope Paul I announcing his appointment to the Frankish Kingdom rather than the Eastern Rome Empire. As such, gradual overtures had been in the process to not only replace the Eastern Roman Empire with the Frankish Kingdom, but also have the Papacy supplant both as the supreme authority of Christendom.

This occurred on Christmas Day 800, with Pope Leo III coronating Charlemagne as the "Emperor of Rome". John Julius Norwich notes that Leo did this since he saw "no living [Roman] Emperor at the time" due to Irene both murdering her own son and being a woman. He therefore took it upon himself to 'create' an emperor and as such continue the Roman Empire through Charlemagne and his Kingdom. That explains the Rome Empire aspect of it, which doesn't stem from the system which the HRE used but rather the conference of the title to Charlemagne.

Now the holy part is two fold for our answer. It acknowledges that the appointment of the Roman Emperor was now subject to the Pope. This institution of papal coronation is the reason that the Empire is holy, as rather than "the emperor’s coronation by the patriarch followed upon election by the army, senate, and the people" as was done in Constantinople, here only the Pope coronated Charlemagne and bound him to "to his own person [Pope Leo III], to the see of St Peter, and to the Holy Roman Republic". This papal coronation established "the imperial crown as his [Pope Leo III] own personal gift" and granted the Pope superiority over the "emperor whom he had created". It should be noted that while it is called Holy now, this would not have been the case in either the coronations of Charlemagne or Otto I, with it likely just being recognized as the Roman Empire.

As such, while the title "Germanic Papal Union" does acknowledge the reality of the systems and culture that existed through the HRE, we do not call it that due to both its creation being linked to the continuation of the Roman Empire, and the fact that while the Eastern Roman Empire was situated around Constantinople, the HRE was heavily tied to Rome itself.

Sources Used:

Ullmann, Walter. “The Coronation and Papal Concepts of Emperorship.” In The Coronation of Charlemagne; What did it signify, ed. Richard E. Sullivan. Boston: D.C. Heath and Company, 1959, 70-79.

Folz, Robert. The Coronation of Charlemagne, trans. J. E. Anderson. London: Routledge & Keagan Paul, 1974.

Norwich, John Julius. Absolute Monarchies. New York: Random House, 2011.

Ohnsorge, Werner. “The Coronation and Byzantium.” In The Coronation of Charlemagne; What did it signify, ed. Richard E. Sullivan. Boston: D.C. Heath and Company, 1959. 80-91