eastern frontier and the Arab borderlands in 856, the imperial government resettled them in Thrace, thus cutting them off from their coreligionists and populating another border region. Michael was also responsible, as per the writings of Constantine VII, for the subjugation of the Slavs settled in the Peloponnese. A conflict between the Byzantines and Bulgarian Empire occurred during 855 and 856. The Byzantine Empire wanted to regain its control over some areas of Thrace, including Philippopolis (Plovdiv) and the ports around the Gulf of Burgas on the Black Sea. Byzantine forces, led by the emperor and the caesar Bardas, were successful in reconquering a number of cities – Philippopolis, Develtus, Anchialus and Mesembria among them – as well as the region of Zagora. At the time of this campaign the Bulgarians were distracted by a war with the Franks under Louis the German and the Croatians. In 853 Boris had allied himself to Rastislav of Moravia against the Franks. The Bulgarians were heavily defeated by the Franks; following this, the Moravians changed sides and the Bulgarians then faced threats from Moravia. Michael III took an active part in the wars against the Abbasids and their vassals on the eastern frontier from 856 to 863, and particularly in 857 when he sent an army of 50,000 men against Emir Umar al-Aqta of Melitene. In 859, he personally led a siege on Samosata, but in 860 had to abandon the expedition to repel an attack by the Rus' on Constantinople. In 863, Petronas defeated and killed the emir of Melitene at the Battle of Lalakaon, and celebrated a triumph in the capital. Ascendency of Bardas and Christianisation of Bulgaria Bardas justified his usurpation of the regency by introducing various internal reforms. Under the influence of both Bardas and Photios, Michael presided over the reconstruction of ruined cities and structures, the reopening of closed monasteries, and the reorganization of the imperial university at the Maganaura palace under Leo the Mathematician. Photios, originally a layman, had entered holy orders and was promoted to the position of patriarch on the dismissal of the troublesome Ignatios in 858. Although a Council of Constantinople in 861 confirmed Photios as patriarch, Ignatios appealed to Pope Nicholas I, who declared Photios illegitimate in 863, leading to the Photian schism. Michael presided over a synod in 867 in which Photios and the three other eastern patriarchs excommunicated Pope Nicholas and