AD 637

Muslim conquest of Persia

Muslim conquest ends Sasanian political control of central Iraq — not Zoroastrianism

Political rule changed far faster than language or religion: Persian stayed in Iraq's government records for roughly another sixty years.

Ctesiphon abandoned

In 637 Muslim troops under Sa'd ibn Abi Waqqas captured the Sasanian capital complex at Ctesiphon. Yazdegerd III, the royal family, nobles and surviving troops fled.

The conquerors seized the royal treasury and the famous royal garden carpet.

The opening had come at al-Qadisiyya, where Sa'd's army defeated the main Sasanian field army under Rostam. That battle's year is disputed — 636 or 637 in the conventional reconstruction, and a revisionist numismatic chronology proposes 634 or 635.

The sawad taken, the chronology unsettled

By the probable battle of Jalula in late 637, Muslim forces had completed the conquest of the Babylonian sawad, the irrigated heartland of central Iraq. Persian resistance continued farther east.

The traditional chronologies for al-Qadisiyya, Ctesiphon and Jalula do not fit together consistently, so their sequence within 637 will not carry day-level precision.

Accounts of Jalula give contradictory dates, commanders, force sizes and casualty totals; only a battle after Ctesiphon and before Nehavand can be treated as secure.

What did not change

There was no event in 637 in which Islam replaced Zoroastrianism. Conversion of Iranian populations to Islam was gradual and limited through the end of the Umayyad period, accelerating after 750.

The new rulers initially retained extensive Sasanian administrative continuity. Persian remained an official language of business in the eastern caliphate, and tradition dates the Arabization of Iraq's fiscal registers to around 697 — six decades after the conquest.

Mesopotamia had been religiously diverse before the conquest; it was not an exclusively Zoroastrian society.

Sources

Researched 23 Aug 2026 7 sources not yet audited Date disputed

How this was checked

Researched from the web into a fact sheet and rewritten from that sheet. This article has not yet had an independent model audit. How the pipeline works →

Date disputed. Sources disagree; the research places it at ~0637.

What the sources leave uncertain

There was no identifiable event in 637 in which Islam “replaced” Zoroastrianism. That wording confuses military conquest with a demographic transformation extending over centuries.
The date of al-Qadisiyya is highly disputed: sources and scholars place it in 636 or 637, while a revisionist numismatic chronology proposes 634 or 635.
Traditional chronologies for al-Qadisiyya, Ctesiphon, and Jalula do not fit together consistently. Their exact sequence within 637 should not be presented with day-level precision.
Accounts of Jalula contain contradictory dates, commanders, force sizes, and casualty totals; only a battle after Ctesiphon and before Nehavand can be treated as secure.