Further Invasions and Reorganization
Greece was raided in Macedonia in 479 and 482 by the Ostrogoths under their king, Theodoric the Great (493-526). The Bulgars also raided Thrace and the rest of northern Greece in 540 and on repeated other occasions. These continuing Bulgar invasions required the Byzantine Empire to build a defensive wall, called the "Anastasian Wall," that extended for some thirty (30) miles, or more, from the city of Selymbria (now Silivri) to the Black Sea. The Huns and Bulgars raided Greece in 559 until the Byzantine army returned from Italy, where Justinian I had been attempting to capture the heart of the Roman Empire.
According to historical documents, the Slavs invaded and settled in parts of Greece beginning in 579 and Byzantium nearly lost control of the entire peninsula during the 580s. However, there is no archaeological evidence indicating Slavic penetration of imperial Byzantine territories before the end of the 6th century. Overall, traces of Slavic culture in Greece are very rare.
The city of Thessaloniki remained unconquered even after being attacked by the Slavs around 615. The Slavs were eventually defeated, gathered by the Byzantines and placed into segregated communities known as Sclaviniae. During the early 7th century, Constans II made the first mass-expulsions of Slavs from the Greek peninsula to the Balkans and central Asia Minor. Justinian II defeated and destroyed most of the Sclaviniae, and moved as many as 110,000-200,000 Slavs from the Greek peninsula to Bithynia, while he enlisted some 30,000 Slavs in his army.
The Slavic populations that were placed in these segregated communities were used for military campaigns against the enemies of the Byzantines. In the Peloponnese, more Slavic invaders brought disorder to the western part of the peninsula, while the eastern part remained firmly under Byzantine domination. Empress Irene organised a military campaign which liberated those territories and restored Byzantine rule to the region, but it was not until emperor Nicephorus I's resettlement of some rural areas of Peloponnese with Greek-speakers from southern Italy, that the last trace of Slavic element was eliminated.
In the mid-7th century, the empire was reorganized into "themes" by the Emperor Constans II, including the Theme of Thrace, the naval Karabisianoi corps in southern Greece and the Aegean islands. The Karabisanoi were later divided by Justinian II into the Theme of Hellas (centred on Corinth) and the Cibyrrhaeotic Theme By this time, the Slavs were no longer a threat to the Byzantines since they had been either defeated numerous times or placed in the Sclaviniae. The Slavic communities in Bithynia were destroyed by the Byzantines after General Leontios lost to the Arabs in the Battle of Sebastopolis in 692 as a result of the Slavs having defected to the Arab side.
These themes rebelled against the iconoclast emperor Leo III in 727 and attempted to set up their own emperor, although Leo defeated them. Leo then moved the headquarters of the Karabisianoi to Anatolia and created the Cibyrrhaeotic Theme of them. Up to this time Greece and the Aegean were still technically under the ecclesiastic authority of the Pope, but Leo also quarreled with the Papacy and gave these territories to the Patriarch of Constantinople. As emperor, Leo III, introduced more administrative and legal reforms than had been promulgated since the time of Justinian. Meanwhile the Arabs began their first serious raids in the Aegean. Bithynia was eventually re-populated by Greeks from mainland Greece and Cyprus.
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