800 Charlemagne goes to Rome to inquire into charges against Leo. Leo crowns him emperor. Foundation of the empire of Charlemagne. The pope and emperor begin the upbuilding of the fabric of the Middle Ages. The pope is subordinate to the emperor.
816 Stephen IV. He is unpopular, and makes the Romans swear fealty to the emperor. Is compelled to take refuge with Louis le Débonnaire. Returns to Rome, and dies.
817 Paschal I. Assumes pontificate without imperial sanction. The Romans, admonished by the emperor, agree not to allow this again.
824 Eugenius II.
827 Valentinus dies in five weeks. Gregory IV. He mediates between Louis le Débonnaire and his sons. His pontificate is uneventful, but materially advances pretensions of the hierarchy.
844 Sergius II consecrated without consent of the emperor Lothair. Lothair sends his son, Louis, with an army to Rome, but his meeting with the pope is amicable. Louis II made king of Lombardy.
847 Leo IV. The Saracens invade Italy as far as the gates of Rome. Driven off by Louis. Leo fortifies a portion of Rome, henceforth known as the Leonine city, including the Vatican and church of St. Peter.
850 The “False Decretals” come to light.
855 Benedict III. His election contested by Anastasius, who, at head of armed faction, seizes the Lateran. The imperial legates decide in favour of Benedict, and Anastasius is expelled. Beginning of the strife between Photius and Ignatius for the see of Constantinople, which ends in the permanent schism between the eastern and western churches.