In 799 he received, at Aix-la-Chapelle, news of serious disturbances which had broken out at Rome; that Pope Leo III had been attacked by conspirators, who, after pulling out, it was said, his eyes and his tongue, had shut him up in the monastery of St. Erasmus, whence he had with great difficulty escaped, and that he had taken refuge with Winigisius, Duke of Spoleto, announcing his intention of repairing thence to the Frankish King.  Leo was already known to Charlemagne; at his accession to the pontificate, in 795, he had sent to him, as to the patrician and defender of Rome, the keys of the prison of St. Peter, and the banner of the city.  Charlemagne showed a disposition to receive him with equal kindness and respect.  The Pope arrived, in fact, at Paderborn, passed some days there, according to Eginhard, and returned to Rome on the 30th of November, 799, at ease regarding his future, but without knowledge on the part of anyone of what had been settled between the King of the Franks and him.  Charlemagne remained all the winter at Aix-la-Chapelle, spent the first months of the year 800 on affairs connected with Western France, at Rouen, Tours, Orleans, and Paris, and, returning to Mayence in the month of August, then for the first time announced to the general assembly of Franks his design of making a journey to Italy.  He repaired thither, in fact, and arrived on the 23d of November, 800, at the gates of Rome.  The Pope “received him there as he was dismounting; then, the next day, standing on the steps of the basilica of St. Peter and amid general hallelujahs, he introduced the King into the sanctuary of the blessed apostle, glorifying and thanking the Lord for this happy event.”  Some days were spent in examining into the grievances which had been set down to the Pope’s account, and in receiving two monks arrived from Jerusalem to present to the King, with the patriarch’s blessing, the keys of the Holy Sepulchre and Calvary, as well as the sacred standard.  Lastly, on the 25th of December, 800, “the day of the Nativity of our Lord,” says Eginhard, “the King came into the basilica of the blessed St. Peter, apostle, to attend the celebration of mass.  At the moment when, in his place before the altar, he was bowing down to pray, Pope Leo placed on his head a crown, and all the Roman people shouted, ’Long life and victory to Charles Augustus, crowned by God, the great and pacific Emperor of the Romans!’ After this proclamation the Pontiff prostrated himself before him and paid him adoration, according to the custom established in the days of the old emperors; and thenceforward Charles, giving up the title of patrician, bore that of emperor and augustus.”

Eginhard adds, in his Life of Charlemagne:  “The King at first testified great aversion for this dignity, for he declared that, notwithstanding the importance of the festival, he would not on that day have entered the church if he could have foreseen the intentions of the sovereign Pontiff.  However, this event excited the jealousy of the Roman emperors (of Constantinople), who showed great vexation at it; but Charles met their bad graces with nothing but great patience, and thanks to this magnanimity which raised him so far above them, he managed, by sending to them frequent embassies and giving them in his letters the name of brother, to triumph over their conceit.”