The Arab Conquests

Between the death of the Prophet Muhammad in 632 and the early years of the eighth century, the Arabs, unified by the new faith of Islam, conquered an enormous arc of territory stretching from the Indus valley in the east to the Atlantic coast of Morocco and the Iberian Peninsula in the west. The Sasanian Persian Empire, the ancient rival of Byzantium and one of the two great powers of late antiquity, was destroyed. The Byzantine Empire lost its wealthy southern and eastern provinces, retaining only Anatolia and a handful of Mediterranean outposts. North Africa, the Iberian Peninsula, and the Iranian plateau passed under Arab rule. By the early eighth century, the caliphate ruled a population comparable to that of the former Roman Empire, and the political and religious map of the Early Middle Ages had been transformed.

The Arab conquests were, by any measure, one of the most extraordinary waves of territorial expansion in pre-modern history. Their speed, scope, and durability have prompted a great deal of historical debate. What explains the rapid collapse of the Byzantine and Sasanian defenses? Why did the conquered populations, in many cases, accept Muslim rule? What was the relationship between religious conviction, economic motive, and political circumstance in the success of the conquests? This article surveys the chronology of the conquests, the principal campaigns, and the broader question of how and why the early Islamic state expanded so quickly.

The Background: Late Antiquity in Crisis

The Arab conquests cannot be understood apart from the condition of the two empires that they overthrew. The Sasanian Empire and the Eastern Roman (Byzantine) Empire had been at war, with brief interruptions, for more than twenty years before the death of Muhammad. The last great war of late antiquity began in 602 when the Sasanian king Khosrow II invaded the Byzantine provinces, took Antioch and Damascus, and by 614 had captured Jerusalem, removing the True Cross to Ctesiphon. The Byzantine emperor Heraclius, taking the throne in 610, spent the next two decades in a costly war of reconquest, restoring the True Cross in 628. The war had been won, but at tremendous cost: the Byzantine armies were exhausted, the treasury was empty, the Syrian and Egyptian populations had been subjected to a Sasanian occupation, and the religious homogeneity of the empire had been disturbed by the Monophysite controversy.

The Sasanian state did not long survive. Khosrow II was deposed in 628, and within a few years the empire was in the grip of civil war, assassinations, and the breakdown of central authority. The Arab armies, taking advantage of the chaos, defeated Sasanian forces at the battles of Qadisiyyah (636) and Nihavand (642) and by 651 had extinguished the Sasanian dynasty. The Arabian Peninsula, which had been caught between the two great powers in the sixth century, found that both of them were now exhausted, and the political vacuum was filled by the armies of the new caliphate.

Sources and Historiography

The sources for the Arab conquests are uneven. The principal Muslim sources, including the works of al-Waqidi, al-Tabari, and Ibn al-Athir, were compiled two or three centuries after the events they describe, and their narratives are shaped by later concerns, including the elaboration of the heroic reputation of the early conquerors. The non-Muslim sources, including the Greek historian Theophanes the Confessor and the Syriac chroniclers, are often closer in time to the events. Archaeology, numismatics, and papyrology have in recent decades provided a wealth of additional evidence, including the papyrus archive of the Arab governor Qurra ibn Sharik, which has illuminated the early Islamic administration of Egypt. Modern scholarship has moved from earlier environmental and zeal-based explanations to emphasize political collapse in the conquered empires, the assimilation of the conquerors, and the importance of trade, taxation, and the consent of the subject populations.

The First Phase: The Conquests of Syria, Palestine, and Iraq

The first major wave of conquests was launched under the caliph Abu Bakr (632-634) and continued under Umar (634-644). The sources preserve a vivid picture of the campaigns: small but mobile Arab armies, supplemented by Bedouin cavalry, attacking the long frontiers of the two empires. The Arabs were not, at first, attempting to occupy the rich provinces of the Byzantine East; they were striking at frontier towns, in the manner of Bedouin raiding, and gathering booty. It was the reaction of the Byzantine and Sasanian empires, in particular the catastrophic Byzantine defeat at the Battle of Yarmuk in 636, that gave the conquests their historical weight.

The Yarmuk, fought in the summer of 636 on the eponymous tributary of the Yarmouk River in the Golan, was the decisive engagement of the early conquests. The Arab forces, commanded by Khalid ibn al-Walid and Abu Ubayda ibn al-Jarrah, met a much larger Byzantine army that had been gathered by the emperor Heraclius. The sources, mixing history with legend, record that a sandstorm blew in the faces of the Byzantine troops. The result was a decisive Arab victory. Within a year, Damascus, Jerusalem (which surrendered in 637), and Antioch (taken in 638) had been occupied. The remainder of Syria, Palestine, and Phoenicia was secured by a series of capitulations in which the major cities accepted Muslim rule in return for the preservation of their lives, property, and - in the case of the Christian holy places - their churches.

The conquest of the Sasanian Empire proceeded in parallel. The decisive battle was the Battle of Qadisiyyah, fought in 636 near al-Hillah in modern Iraq, in which the Arab army defeated a Sasanian force. Ctesiphon, the Sasanian capital, was taken in 637. The Sasanian king Yazdegerd III fled eastward, and the last Sasanian forces were defeated at the Battle of Nihavand in 642. The conquest of Iran was completed over the following decades, with major centers such as Isfahan, Rayy, and the plateau cities submitting to Arab rule.

The Conquest of Egypt

The conquest of Egypt was carried out between 639 and 642, primarily by the army of Amr ibn al-As, the general sent by the caliph Umar. The Byzantine province of Egypt was one of the wealthiest in the empire, and its capital, Alexandria, was a center of Hellenistic learning and of the grain supply of Constantinople. The Arab army entered Egypt in late 639, taking the frontier town of Pelusium and advancing into the Nile Delta. The Byzantine garrison, supplemented by reinforcements from Constantinople, was defeated at the Battle of Heliopolis in 640, and the Arab army laid siege to the fortress of Babylon (Old Cairo) and then to Alexandria itself. The Byzantine patriarch Cyrus negotiated a surrender in November 641, in return for the safe withdrawal of the Byzantine garrison. The surrender, which became the model for later capitulations in North Africa, preserved the lives and property of the inhabitants, the integrity of the churches, and the agricultural economy of the province.

The Arab conquest of Egypt had several long-term consequences. It severed the grain supply to Constantinople, contributing to the Byzantine state’s chronic fiscal difficulties. It added to the caliphate a wealthy and densely populated province. And it gave the new Arab garrison of Fustat (the predecessor of Cairo) a strategic position from which to launch further campaigns in North Africa.

The Conquests of North Africa and Iberia

The conquest of the remainder of North Africa took the better part of a century. The Arab armies advanced westward across the Byzantine and Vandal territories, founding the great mosque of Kairouan in 670 as a base for further operations. The Berber populations of North Africa accepted Islam in large numbers, and the Berber converts provided the manpower for the Arab-Berber invasion of the Iberian Peninsula in 711. The crossing into Visigothic Spain, led by Tariq ibn Ziyad and Musa ibn Nusayr, defeated the last Visigothic king Roderic at the Battle of Guadalete in 711 and within a few years had overrun most of the peninsula. The Arab advance into Gaul was finally checked at the Battle of Tours in 732, in which the Frankish mayor of the palace Charles Martel defeated a raiding army under Abd al-Rahman al-Ghafiqi.

The Eastern Conquests: Iran, Central Asia, and Sindh

The Arab conquest of Iran was completed in the mid-seventh century, but the conquest of Central Asia and the Indus Valley was a longer process. The Arab armies crossed the Oxus into Transoxiana in the eighth century, taking Bukhara, Samarkand, and Khwarazm in a long and fitful war with the local Iranian, Sogdian, and Turkic rulers. The conquest of Sindh, in modern Pakistan, was carried out under the Umayyad and early Abbasid caliphs by the armies of Muhammad ibn al-Qasim and others. By the time of the early Abbasid caliphs, the caliphate stretched from the Atlantic to the Indus.

The Organization of the Conquest Armies

The Arab armies of the conquests were, by late antique standards, relatively small but highly mobile. The early sources speak of forces of 6,000 to 18,000 men, and the armies of the conquests were probably never larger than 30,000 or 40,000. Their success depended on speed, on the ability to live off the land, and on the morale and discipline of soldiers who were fighting, in many cases, for religious reward as well as for booty. The military system was tribal, with the units organized by clan and tribe, and the soldiery of each garrison town received a share of the revenues of the province in which they served.

The Muslim conquests were facilitated by the collapse of the central military and administrative systems of the Byzantine and Sasanian empires. The Arab armies were also able to take advantage of the divisions within the conquered populations, including the Monophysite Christians of Syria and Egypt, who had been persecuted by the Chalcedonian Byzantine establishment, and the Zoroastrian and other non-Christian subjects of the Sasanians, who were willing to accept a new regime in place of the old.

The Treatment of the Conquered Populations

The treatment of the conquered populations was governed, in theory, by the rules of the early capitulations. The non-Muslim inhabitants, known as dhimmis, were granted the right to practice their religion, to retain their property, and to be governed by their own personal status laws. In return, they were required to pay a poll tax (jizya) and, in some cases, a land tax (kharaj), and to accept certain social disabilities. The terms of the capitulations varied in practice, and the application of the dhimma differed from region to region.

The conversion of the subject populations to Islam was a slow process. The Arab conquerors generally avoided settlement in the rural countryside, where the indigenous populations might absorb them, and instead settled in new garrison towns such as Kairouan, Fustat, and Kufa. Conversion was accelerated in the eighth and ninth centuries by economic incentives, by the breakdown of the fiscal privileges of non-Muslims, and by the assimilation of the new Muslim communities to the surrounding populations. By the tenth and eleventh centuries, the majority of the population of the caliphate in the central Islamic lands was Muslim, although substantial Christian, Jewish, and Zoroastrian communities remained in various parts of the caliphate until much later.

The Significance of the Conquests

The Arab conquests transformed the Early Middle Ages. They destroyed the Sasanian Empire. They reduced the Byzantine state to a Greek-speaking, Anatolian rump forced to adapt to a fundamentally new strategic situation. They brought the rich provinces of the southern and eastern Mediterranean, with their long traditions of classical civilization, into the political orbit of the new Arabic-speaking caliphate. They created a vast, multilingual, and religiously plural empire in which the resources, ideas, and trade goods of Asia, Africa, and Europe were combined in a new political and cultural synthesis.

The early caliphs presided over a state that, in many respects, was a continuation of the late antique empires it had supplanted. The fiscal system, the postal and intelligence services, and the architectural and administrative practices of the caliphate drew heavily on the inheritance of the Sasanian and Byzantine empires. The Arabic language gradually became the language of administration, scholarship, and trade across the caliphate, but the new Islamic civilization was built on the shoulders of the late antique and Hellenistic traditions the Arabs inherited. The early caliphate was, in this sense, both a revolutionary and a conservative state: revolutionary in the religious and political transformation it brought, conservative in its use of the late antique administrative, fiscal, and cultural inheritance.