The Muslim Conquest of Persia

The Muslim conquest of Persia was the series of military campaigns in which the armies of the early Islamic state, led by the caliphs in Medina, overthrew the Sasanian Empire. The Sasanians had ruled Iran and Iraq since the third century CE and were one of the two great powers of late antiquity, alongside the Roman (Byzantine) Empire.

The conquest happened in stages. Arab forces first raided and occupied parts of southern Iraq in the 630s, won a decisive battle at al-Qadisiyyah, captured the Sasanian capital Ctesiphon, and then, after the Battle of Nahavand in 642, advanced across the Iranian plateau. The last Sasanian king, Yazdegerd III, was killed in 651.

Military conquest was fast, but social and religious change was slow. Iran became part of the caliphate, but the majority of its people probably did not become Muslims until the ninth or tenth century. The Persian language survived and, in a new form written in Arabic script, became one of the great languages of Islamic civilisation.

From 602 to 628 the Sasanians and the Byzantines fought one of the longest and most exhausting wars of the ancient world. At first the Persian king Khosrow II conquered Syria, Palestine and Egypt, but the Byzantine emperor Heraclius struck back deep into Persian territory. In 628 Khosrow was overthrown and killed by his own nobles.

Several years of chaos followed. In about four years, more than half a dozen rulers — including two queens, Boran and Azarmidokht — came and went. A plague struck the empire. Great noble families competed for power, and some regions were only loosely controlled by the court. In 632 the young Yazdegerd III was placed on the throne.

The Sasanians had also weakened their own desert frontier. For generations the Arab Lakhmid kings of al-Hira had guarded the edge of Iraq for Persia, but around 602 Khosrow II deposed and later killed the last Lakhmid king, al-Nuʿman III. Soon afterwards, probably around 609, Arab tribes defeated a Sasanian force at Dhi Qar, a clash later remembered in Arabic tradition as a sign that Persian power could be broken.

At the same moment, the Arabian Peninsula had been united under the Prophet Muhammad and, after his death in 632, under the first caliph Abu Bakr, who suppressed tribal revolts in the Ridda Wars. This created a powerful new force on the border of two exhausted empires.

The conquering armies were made up mostly of Arab tribesmen, organised by the government in Medina under the caliphs Abu Bakr (632–634), ʿUmar (634–644) and ʿUthman (644–656). Their soldiers were motivated by the new faith, by the promise of pay and booty, and by tribal loyalty. Some Arab tribes of Iraq that had lived under Sasanian influence, such as the Banu Shayban, joined early.

The Sasanian side included the royal army with its heavily armoured cavalry and war elephants, the forces of great noble houses, and regional lords and garrisons. Loyalties were not always firm: some Persian commanders and local elites negotiated surrender terms, and some Persian units, such as the Asawira cavalry, went over to the Arabs and settled among them.

Many inhabitants of Iraq and Iran were not Zoroastrian Persians but Aramaic-speaking Christians, Jews, and other communities. For some of them, the change of rulers mattered less than the terms they could negotiate for taxes and protection.

In 633 Khalid ibn al-Walid, together with the local leader al-Muthanna ibn Haritha, led campaigns in the lower Euphrates region and took the town of al-Hira. Khalid was then sent to Syria to fight the Byzantines. In 634 a Sasanian army defeated the Arabs at the Battle of the Bridge, but the Arabs soon recovered.

Caliph ʿUmar sent a larger army under Saʿd ibn Abi Waqqas. At al-Qadisiyyah, south-west of al-Hira, the Arabs defeated the main Sasanian army commanded by Rostam Farrokhzad, who was killed. The battle is usually dated to 636, but the sources disagree and dates from 635 to 638 have been proposed. Arab tradition says the great royal banner, the Derafsh Kaviani, was captured.

The Arabs then crossed the Tigris and took Ctesiphon, the Sasanian capital, in 637, seizing its vast treasures. Yazdegerd fled east. A further victory at Jalula later in 637 opened the way to the Zagros Mountains. To control Iraq, the conquerors founded new garrison cities, Basra and Kufa, where Arab soldiers and their families settled and which became centres of early Islamic culture. Later Arabic and Persian writers often reflected on the ruins of Ctesiphon’s palace as a lesson about the passing of worldly power.

The Arabs next conquered Khuzistan, in south-western Iran, where the Persian general Hormuzan resisted for several years before surrendering. Yazdegerd gathered a new army, but it was defeated at Nahavand in the Zagros in 642. Arabic tradition called this “the victory of victories”, because after it the Sasanians could no longer field a large royal army.

Over the following years Arab forces advanced city by city: Hamadan, Isfahan, Rayy, Fars with the old royal centre of Istakhr, Kerman, Sistan and Khorasan. Many cities surrendered on terms, promising tribute; some rebelled and were reconquered. Fars and Istakhr in particular resisted fiercely and suffered heavy losses when they were retaken.

Yazdegerd moved from place to place, increasingly losing the support of local governors. In 651 he was killed near Merv in Khorasan. According to a well-known tradition, he was murdered by a miller in whose mill he was hiding, possibly at the instigation of the local governor. His son Peroz sought help from Tang China, which gave him titles and refuge, but the Sasanian restoration never came.

The death of Yazdegerd did not mean that all of Iran was under firm control. Many cities that had surrendered on terms revolted when the first Muslim civil war (656–661) distracted the caliphate, and had to be conquered again under the Umayyads. Khorasan, with its great oasis city of Merv, became the base for Arab armies moving further east into Central Asia; Arab families were settled there in large numbers from the 670s.

In the mountains south of the Caspian Sea, Tabaristan and neighbouring regions were ruled by local dynasties — some claiming Sasanian descent — who paid tribute at times but kept their independence and Zoroastrian religion into the mid-eighth century and, in some valleys, longer. In the east, local princes in Sistan and in what is now Afghanistan resisted for decades.

The Sasanian heir Peroz and later his son stayed for years at the Tang court and on its western frontier. Tang China created a nominal “Persian” military command for Peroz around 661, but it never became a real base for reconquest. Their story shows how the fall of the Sasanians was felt across Eurasia, as far as Chang’an, where Persian refugees, merchants and priests formed communities.

Many cities and districts came under Muslim rule through agreements (sulh) rather than storming. Such treaties typically guaranteed the lives, property and religion of inhabitants in return for tribute and taxes. Places taken by force could suffer killing, enslavement and confiscation. The sources report both kinds of outcome, sometimes for the same city in different versions.

Casualty figures cannot be established. Early Arabic accounts often give large and symbolic numbers for battles, and later Persian traditions stress destruction and humiliation. Historians agree that the conquest brought deaths, enslavement of prisoners and deportations, but also that many ordinary farmers and townspeople continued their lives under new masters, often with the same local Persian landowners (dehqans) collecting taxes.

Zoroastrians, Christians and Jews were generally recognised as protected peoples (dhimmis) who paid a poll tax (jizya) and kept their religions. Over time, social and economic pressures, as well as sincere attraction to Islam, encouraged conversion. Some Zoroastrian communities later migrated; the ancestors of the Parsis of India are traditionally said to have left Iran some centuries after the conquest, though the date and circumstances are debated.

In the short term, the conquest doubled the resources of the caliphate. The wealth of Iraq and Iran, and the Sasanian administrative tradition, helped support the new Islamic state. The early caliphs used Sasanian-style coins, often with the image of a Sasanian king and a short Arabic phrase added, and kept many Persian officials and procedures.

Iran was not simply absorbed. In mountainous areas such as Tabaristan near the Caspian Sea, local dynasties kept their independence for more than a century. Persian converts, known as mawali (clients), resented Arab privilege, and many supported the Abbasid revolution of 747–750, which began in Khorasan. Under the Abbasids, with their capital Baghdad not far from ruined Ctesiphon, Persian ideas of kingship and administration strongly influenced the caliphate.

Culturally, the most striking result was that Persian survived. From the ninth and tenth centuries, New Persian, written in Arabic script with many Arabic words, became a literary language at courts such as that of the Samanids in Bukhara. The poet Ferdowsi completed the Shahnameh around 1010, retelling Iran’s legendary and Sasanian history and ending with the Arab conquest. Iran became a major centre of Islamic learning, and later the heartland of Shiʿi Islam.

In early Arabic historical writing, the conquest of Persia was part of the futuh — the “openings” of lands to Islam — told as a sign of divine favour. Stories of heroic warriors, of pious simplicity defeating Persian luxury, and of Persian envoys amazed by Arab faith became part of Islamic tradition.

In Persian literary memory the event was a tragedy. The Shahnameh presents the fall of the Sasanians as the end of an age, with a famous letter of the general Rostam lamenting what is to come. In the ninth and tenth centuries the Shuʿubiyya movement defended the dignity of non-Arab, especially Persian, culture within Islam. Modern Iranian nationalism in the late nineteenth and twentieth centuries, especially under the Pahlavi monarchy, often idealised pre-Islamic Iran and described the conquest as a national disaster, while Islamic perspectives — dominant in Iran since 1979 — stress that Iranians embraced Islam and enriched it.

The memory has also been politicised elsewhere. During the Iran–Iraq War (1980–1988), the Iraqi government under Saddam Hussein called its war against Iran a new “Qadisiyyah”, using the ancient victory as Arab nationalist propaganda. Historians caution against reading modern ideas of nations — “Arabs” versus “Persians” — back into the seventh century, when identities were shaped by religion, tribe, region and class.

Most of our narrative comes from Arabic histories written two centuries or more after the events, especially al-Tabari’s great History of the Prophets and Kings (early tenth century) and al-Baladhuri’s Futuh al-Buldan (Conquests of the Lands, ninth century). These works collect earlier oral and written reports, each with a chain of transmitters. Many reports about Iraq in al-Tabari come from Sayf ibn ʿUmar, whose accounts are vivid but have been criticised by modern scholars for exaggeration and tribal bias.

Non-Muslim sources written closer to the events are rare but precious. The Armenian History attributed to Sebeos, written in the second half of the seventh century, gives the earliest major outside account of the conquests. A short Syriac chronicle known as the Khuzistan Chronicle, from about the 660s, also mentions the fighting. Middle Persian Zoroastrian texts written later preserve apocalyptic laments about the loss of Iranian kingship.

Material evidence helps test the texts: coins (including Arab-Sasanian issues), seals, papyri and archaeological evidence from cities such as Ctesiphon, Kufa and Istakhr. These show continuity in administration and town life as well as signs of disruption.

How did a young state defeat an ancient empire so quickly? Explanations include Sasanian exhaustion after the war with Byzantium, plague and civil strife; the mobility and motivation of Arab armies; skilled leadership from Medina; and the willingness of local elites to negotiate. Fred Donner’s The Early Islamic Conquests (1981) emphasised the role of the new Islamic state in organising the tribes, while Hugh Kennedy’s The Great Arab Conquests (2007) offers a narrative that balances Arab and Iranian perspectives.

Parvaneh Pourshariati’s Decline and Fall of the Sasanian Empire (2008) argues that the empire was effectively a confederation in which great Parthian noble families shared power with the Sasanian house; their conflicts with the court and their separate deals with the Arabs explain much of the collapse. She also proposes a revised, earlier chronology for the conquest of Iraq. Her arguments have been influential but also debated, especially her use of the sources.

On religious change, Richard Bulliet’s Conversion to Islam in the Medieval Period (1979), based on the spread of Muslim names in biographical dictionaries, suggested that conversion in Iran was slow at first and accelerated in the ninth century, with a large Muslim majority only by around the tenth or eleventh century. His method has been criticised, but his broad picture of gradual conversion is widely accepted. Scholars also debate how far the early Arabic conquest narratives are historical records rather than later literary and legal constructions.