From Crisis to Conquest: Byzantium's Medieval Centuries and the Fall of Constantinople

Between 602 and 619 CE, the Sasanian Empire under Khosrow II invaded the Byzantine territories of Syria, Palestine, and Egypt, capturing Jerusalem in 614 CE and occupying Egypt, the empire's granary, around 619 CE. From 622 CE the emperor Heraclius launched a counteroffensive that penetrated deep into Sasanian territory, and a decisive Persian defeat at the Battle of Nineveh in 627 CE forced the fall of Khosrow II and brought peace between the two empires in 628 CE. Both powers emerged economically and militarily exhausted after more than two decades of total war, a mutual exhaustion that facilitated the Arab conquests that followed: the Battle of the Yarmuk River in 636 CE delivered a decisive Byzantine defeat in Syria, Egypt fell to the Arabs between 639 and 642 CE, and Byzantium permanently lost its richest provinces in the Near East and North Africa within a few decades. In response, the empire developed the theme system, dividing its remaining territory into military-administrative districts in which soldiers, called stratiotai, received land grants in exchange for hereditary military service.