When the Roman Prefecture of Illyricum was divided between the East and West Roman Empires in 379, Thessaloniki became the capital of the new Prefecture of Illyricum (reduced in size). Its importance was second only to Constantinople itself, while in 390 it was the location of a revolt against the emperor Theodosius I and his Gothic mercenaries. Butheric, their general, together with several of his high officials, were killed in an uprising triggered by the imprisoning of a favorite local charioteer for pederasty with one of Butheric's slave boys. 7,000 - 15,000 of the citizens were massacred in the city's hippodrome in revenge – an act which earned Theodosius a temporary excommunication. A quiet interlude followed until repeated barbarian invasions after the fall of the Roman Empire, while a catastrophic earthquake severely damaged the city in 620, resulting in the destruction of the Roman Forum and several other public buildings. Thessaloniki itself came under attack from Slavs in the 7th century (most notably in 617 and 676–678); however, they failed to capture the city. Byzantine brothers Saint Cyril and Saint Methodius were born in Thessaloniki and it was Byzantine Emperor Michael III who encouraged them to visit the northern regions as missionaries where they adopted the South Slavonic speech as the basis for the Old Church Slavonic language. In the 9th century, the Byzantines decided to move the market for Bulgarian goods from Constantinople to Thessaloniki. Tsar Simeon I of Bulgaria subsequently invaded Thrace, defeated a Byzantine army and forced the empire to move the market back to Constantinople. In 904, Saracens, led by Leo of Tripoli, managed to seize the city and after a ten-day depredation, left after having freed 4,000 Muslim prisoners while capturing 60 ships, and gaining a large loot and 22,000 slaves, mostly young people. Following these events, the city recovered and the gradual restoration of Byzantine power during the 10th, 11th, and 12th centuries brought peace to the area. As the population of the city expanded, according to Benjamin of Tudela, a Jewish community of some 500-strong was also established in the 12th century. During that time the city came to host the fair of Saint Demetrius every October, which was held just outside the city walls and lasted six days. The economic expansion of the city continued throughout the 12th century as the rule of the Komnenoi emperors expanded Byzantine control into Serbia and Hungary, to the north.