of any bishop who refused to answer a summons to Rome. Faced with this decree, Hilary submitted to the pope, although under his successor, Ravennius, Leo divided the metropolitan rights between Arles and Vienne (450). In 445, Leo disputed with Patriarch Dioscorus, Cyril of Alexandria's successor as Patriarch of Alexandria, insisting that the ecclesiastical practice of his see should follow that of Rome on the basis that Mark the Evangelist, the disciple of Peter the Apostle and the founder of the Alexandrian Church, could have had no other tradition than that of the prince of the apostles. The fact that the African province of Mauretania Caesariensis had been preserved to the empire and thus to the Nicene faith during the Vandal invasion and, in its isolation, was disposed to rest on outside support, gave Leo an opportunity to assert his authority there. In 446 he wrote to the Church in Mauretania in regard to a number of questions of discipline, stressing the point that laymen were not to be appointed to the episcopate. In a letter to the bishops of Campania, Picenum, and Tuscany (443) he required the observance of all his precepts and those of his predecessors; and he sharply rebuked the bishops of Sicily (447) for their deviation from the Roman custom as to the time of baptism, requiring them to send delegates to the Roman synod to learn the proper practice. Because of the earlier line of division between the western and eastern parts of the Roman Empire, Illyria was ecclesiastically subject to Rome. Pope Innocent I had constituted the metropolitan of Thessalonica his vicar, in order to oppose the growing influence of the patriarch of Constantinople in the area. In a letter of about 446 to a successor bishop of Thessalonica, Anastasius, Leo reproached him for the way he had treated one of the metropolitan bishops subject to him; after giving various instructions about the functions entrusted to Anastasius and stressing that certain powers were reserved to the pope himself, Leo wrote: "The care of the universal Church should converge towards Peter's one seat, and nothing anywhere should be separated from its Head." He succeeded in having an imperial patriarch, Timothy Salophakiolos, and not Timotheus Aelurus, chosen as Coptic Orthodox Pope of Alexandria on the murder of Greek Patriarch Proterius of Alexandria. Writings Almost 100 sermons and 150 letters of Leo I have been preserved. Tome