Fifteen Years
Persia: Empire and AfterwardsAn Empire at Its Weakest
The Sassanid empire that met the Arab armies in the 630s had just finished a war with Byzantium that lasted a quarter of a century. Both sides had exhausted themselves; both had spent treasure and manpower they could not replace. Persia had then gone through a succession crisis so severe that a dozen claimants held the throne in four years, some for a matter of weeks. Plague had passed through. The timing was catastrophic.
Qadisiyyah
The decisive battle was fought at al-Qadisiyyah, near the Euphrates, around 636. The accounts are later than the events and the numbers in them cannot be trusted, but the outcome is not in doubt: the Sassanid field army was destroyed and its commander Rostam killed. Ctesiphon, the capital, fell the following year.
Nihavand and the End
The last organised resistance ended at Nihavand around 642, remembered in Arabic sources as the victory of victories. Yazdegerd III, the last Sassanid king, fled east across his own empire looking for support and was killed near Merv in 651 — by a miller, according to the tradition, for the money he carried. An empire of four centuries, and a Persian imperial line reaching back to Cyrus, ended with a murder for a purse.
What Actually Changed, and When
The conquest was fast; the conversion was not. For a long period after 651 most people in Iran remained Zoroastrian, paying a tax as protected non-Muslims. Estimates vary, but the shift to a Muslim majority is generally placed some two to three centuries after the conquest, not at it. The empire fell in fifteen years. The society took ten times as long to change.
The Administration Did Not Fall
The new rulers had a vast, functioning bureaucracy in front of them and no apparatus of their own to replace it. For decades the tax registers of Iran and Iraq continued to be kept in Persian by Persian officials, because those were the men who knew how. The Umayyads eventually shifted the registers to Arabic — but by then Persian administrative practice, court ceremony and titles had been absorbed, and the Abbasid caliphate that followed looked far more like a Sassanid court than an Arabian one.
Key Dates to Remember
- 602–628 — The last great Byzantine–Sassanid war exhausts both
- 628–632 — Succession crisis: a dozen claimants in four years
- c. 636 — Qadisiyyah — the field army destroyed
- 637 — Ctesiphon falls
- c. 642 — Nihavand ends organised resistance
- 651 — Yazdegerd III killed near Merv