III.

The Empire Besieged

The empire had survived Germanic and Hunnic tribal migrations and raids in the 5th and 6th centuries and had stabilized a reasonably secure eastern frontier against the Sassanian Empire of Persia, but it could not recover, hold, and govern the entire Mediterranean world. During the second half of the 6th century the Lombards invaded and gradually occupied much of former Byzantine Italy—except for Rome, Ravenna, Naples, and the far south—while Turkic Avar cavalry raided and depopulated much of the Byzantine Balkans.

Many features of the empire and its culture changed during the 7th century. Most of the Balkans were lost to the Avars and to Slavic tribes, who resettled abandoned sites. Meanwhile, the assassination of Mauricius, the first Byzantine emperor to fall to a violent death, led to civil and external war. Emperor Heraclius finally terminated a long series of wars with the Persians by a decisive victory in 628 and the recovery of Persian-occupied Syria, Palestine, and Egypt. Exhaustion from this struggle and bitter religious disputes between rival Christian sects weakened Byzantine defenses and morale, leaving the empire unprepared to face another danger in the decade that followed. Between 634 and 642, Arabs, inspired by a new religion, Islam, conquered Palestine, Syria, Mesopotamia, and Egypt. Constantinople weathered major Arab sieges in the 670s and in 717-18, and Byzantine Asia Minor survived almost annual Arab raids. Byzantium, by a process that remains controversial among historians, transformed its armies into an elite expeditionary guard named tagmata and into army corps called themes (themata). Each was commanded by a strategos, or general, who acquired civil and military authority over his army district; thematic armies became army corps districts, and their soldiers, who acquired tax-exempt lands, preserved the core of the empire while avoiding the ruinous drain of cash that had overstrained the salaried armies of the period before the Arab invasions. Urban life and commerce declined except in Thessaloníki and Constantinople. Warfare and resulting insecurity inhibited agriculture and education. The empire, with limited resources, could no longer maintain the full dimensions, infrastructure, and complexity of the late Roman Empire. It managed to endure and adapt to its straitened circumstances.