In 799, Pope Leo III had been mistreated by the Romans, who tried to put out his eyes and tear out his tongue. Leo escaped and fled to Charlemagne at Paderborn, asking him to intervene in Rome and restore him. Charlemagne, advised by Alcuin of York, agreed to travel to Rome, doing so in November 800 and holding a council on 1 December. On 23 December Leo swore an oath of innocence. At Mass, on Christmas Day (25 December), when Charlemagne knelt at the altar to pray, the Pope crowned him ‘’Imperator Romanorum’’ (“Emperor of the Romans”) in Saint Peter’s Basilica. In so doing, the Pope was effectively nullifying the legitimacy of Empress Irene of Constantinople:
:“When ”/campaign/charlemagne/wikis/Odoacer/new" class=“create-wiki-page-link”>Odoacer compelled the abdication of Romulus Augustulus, he did not abolish the Western Empire as a separate power, but cause it to be reunited with or sink into the Eastern, so that from that time there was a single undivided Roman Empire… [Pope Leo III and Charlemagne], like their predecessors, held the Roman Empire to be one and indivisible, and proposed by the coronation of [Charlemagne] not to proclaim a severance of the East and West… they were not revolting against a reigning sovereign, but legitimately filling up the place of the deposed Constantine VI… [Charlemagne] was held to be the legitimate successor, not of Romulus Augustulus, but of Constantine VI…"<ref>James Bryce, 1st Viscount Bryce, ‘’The Holy Roman Empire’’, 1864, pg 62–64</ref>
Charlemagne’s coronation as Emperor, though intended to represent the continuation of the unbroken line of Emperors from Augustus to Constantine VI, had the effect of setting up two separate (and often opposing) Empires and two separate claims to imperial authority. For centuries to come, the Emperors in the West would claim sovereignty over both West and East with the Emperors in the East claiming the same.
Einhard says that Charlemagne was ignorant of the Pope’s intent and did not want any such coronation:
[H]e at first had such an aversion that he declared that he would not have set foot in the Church the day that they [the imperial titles] were conferred, although it was a great feast-day, if he could have foreseen the design of the Pope.A number of modern scholars, however,<ref>Tierney, Brian. ‘’The Crisis of the Church and State 1050–1300’’. University of Toronto Press, 1964. p. 17.</ref> suggest that Charlemagne was indeed aware of the coronation; certainly he cannot have missed the bejeweled crown waiting on the altar when he came to pray.
In any event, Charlemagne used these circumstances to claim that he was the renewer of the Roman Empire, which had apparently fallen into degradation under the Byzantines. In his official charters, Charles preferred the style ‘’Karolus serenissimus Augustus a Deo coronatus magnus pacificus imperator Romanum gubernans imperium’‘<ref>Cf. ’’Monumenta Germaniae Historica‘’, Diplomata Karolinorum I, 77ff.; title used from 801 onward.</ref> (“Charles, most serene Augustus crowned by God, the great, peaceful emperor ruling the Roman empire”) to a more direct ’’Imperator Romanorum’’ (“Emperor of the Romans”).