LEO IV, pope, saint. — He was ordained a priest by Sergius II, who also elevated him to the cardinalate, with the title of SS. Quattro Coronati; he was elected pope on 27 January 846 and consecrated at Easter (10 April), without the ratification of the emperor Lothar, to whom the gravity of the Roman situation, including the very recent Saracen incursions (846), was offered as an excuse. To remedy this, Leo, taking up an old plan, began restoring the walls around the Vatican as far as Castel S. Angelo (848), creating what he called the Leonine City, solemnly inaugurated on 27 June 852. Following the victory over the Saracens (achieved in 849 near Ostia by the ships of Naples, Amalfi, and Gaeta, which Leo had blessed, thus placing himself on the path that would lead to the holy war), the Pope was able to have a new port built (Leopolis) to replace Centumcellae, which had been destroyed by the infidels.
Leo’s relations with the emperors were not likely to have been very good, given that he did not welcome imperial interference in the Holy See: indeed, after consecrating Louis II (April 850), he obtained from the Carolingians the restoration of canonical prescriptions regarding papal elections. Further and more serious disagreements are revealed by Louis II’s sudden arrival in Rome (855), hastening to prevent the party hostile to the primacy of the papacy, led by some monks and by Alberic himself, the master of Rome and nephew of Theophylact. The few surviving bulls of this Pope are almost all addressed to the monasteries of Cluny and Subiaco and concern donations and privileges. Leo maintained good relations with Alberic, which later deteriorated under subsequent popes. Finally, mention should be made of an act directed to the German bishops with various provisions on marriages between blood relatives, on the recitation of prayers in the Mass, and on communion against sorcerers and soothsayers.