Four centuries of border war after Yarmuk’s shock
From the seventh to the eleventh centuries, successive Islamic caliphates and Byzantium fought for the eastern Mediterranean. After Yarmuk, Arab armies stripped the empire of Levant, Egypt, and North Africa within decades. Later the frontier froze at the Taurus, then swung back as Macedonian emperors reclaimed islands and Syrian footholds.
The first surge came under the Rashidun caliphs in the 630s, when exhausted Byzantium and Persia were still reeling from their own long wars and Justinianic plague. Syria fell by 639 and Egypt by 642; the African exarchate crumbled between 647 and 670 as Arab fleets began probing the seas. Two failed sieges of Constantinople slowed the avalanche, after which the military border settled along Asia Minor’s Taurus range—heavily fortified, constantly raided, and emptied of ordinary settlement by the grind of seasonal war.
When Abbasids replaced Umayyads in 750 they proved less hungry for continental conquest, yet almost yearly clashes continued into the mid-tenth century. Vassals took Crete in 827 and chewed through Sicily from 831 to 878, while ninth- and early tenth-century fleets harried Italian and Dalmatian coasts. Abbasid turmoil after 861 opened space for a Byzantine rebound under the Macedonian dynasty: roughly 920 to 976 saw Anatolian counteroffensives, recoveries in northern Syria and Armenia, and Crete’s reconquest in 961. By century’s end Fatimids, not Abbasids, were the main Arab rival.
The decisive blows fell quickly. Heraclius, too ill to take the field, saw his armies beaten at Ajnadayn in 634 and then at Yarmuk in 636, where the Muslims drew the Byzantines into the pitched battle they normally avoided and turned steep valleys into a killing ground. Jerusalem surrendered in April 637 after a long siege, Antioch fell late that year, and 'Amr ibn al-A'as crossed into Egypt with 3,500 to 4,000 men around the turn of 640, taking Alexandria by September 642.
Losing Egypt cut Byzantium off from its wheat, bringing shortages that weakened its armies for decades. At sea the newcomers raided Sicily in 652 and took Cyprus and Crete a year later, though Crete returned to imperial hands until the 820s. In Africa, Abd Allah ibn Sa'd's invasion of 647 killed the self-proclaimed emperor Gregory and extracted a promised yearly tribute of some 300,000 nomismata, and Carthage itself was destroyed between 695 and 698.
Source: Arab–Byzantine wars
