"In four departments," says Bury, "Justinian has won immortal fame. In warfare, in architecture, in law and in Church history." To him the world owes St. Sofia. He and his uncle Justin both strove against the schism between the Roman and Byzantine Churches, and he was powerful enough to carry a measure which tended to unity by modifying, the Synod of Chalcedon without breaking with Rome. And he prided himself upon speaking Latin. Yet there are those to-day who would hand over his Church of the Holy Wisdom to Greek propagandists. He dealt the final blow at Paganism and denounced the Manicheans--of whom we shall hear much later--and enacted severe laws against them. The history of modern Bosnia begins in Justinian's reign. The Slavs then began to threaten the Empire. Tribes began to drift across the Danube and settle in groups already in the fifth century, but were stopped for a while by the Huns and Ostrogoths, who swept over the Peninsula and infested Illyria and Epirus. "The departure of the Ostrogoths," says Bury, "was like the opening of a sluice. The Slavs and Bulgars, whom their presence had held back, were let loose on the Empire. . . . The havoc made by these barbarians was so serious that Justinian made new lines of defence." In 548 and 551 A.D. masses of Slavs ravaged the land. "The massacres and cruelties committed by these barbarians," says Bury, "make the readers of Procopius shudder." The readers of the Carnegie report of 1913 do likewise. Among the fortresses built by Justinian was Singidunum, now Belgrade, which, founded to hold back the Slav, is now his capital. The invading Slavs were pagan, the natives largely Christian. "The Christians," says Presbyter Diocleas, "seeing themselves in great tribulation and persecution, began to gather on the mountains and tried to construct castles and strongholds that they might escape from the hands of the Slavs until God should visit and liberate them." This is probably the origin of the Vlach settlements on hill-tops and the Albanian mountain strongholds. "The year 581," says John of Ephesus, "was famous for the invasion of the accursed Slavonians . . . who captured cities and forts, and devastated and burnt, reducing the people to slavery, and made themselves masters of the country and settled it by main force. Four years have elapsed and still they live in the land . . . and ravage and burn." The Romans and their civilization were swept coastward, and in Dalmatia their civilization never quite died out. In later times the term "Romanes" was used in a special sense to denote the Romans who maintained their independence against the Slavs. Ragusa and Cattaro are some of the towns they founded.