Battle of Nahāvand
642 CE.
Shown on the map at 31.583°, 44.500°.
The Battle of Nahavand (Arabic: معركة نهاوند Maʿrakah Nahāwand, Persian: نبرد نهاوند Nabard-e Nahâvand), also spelled Nihavand or Nahawand, was fought in 642 between the Rashidun Muslim forces under An-Numan ibn Muqarrin and Sasanian army under King Yazdegerd III. Yazdegerd escaped to the Merv area, but was unable to raise another substantial army. The battle ended in a victory for the Rashidun Caliphate and the Sasanids consequently lost the surrounding cities including Spahan (Isfahan). The engagement resulted in a catastrophic defeat for the Sasanid forces and marks the end of organized Sasanid resistance. Thus opening the path for Islamic expansion into Persia and the subsequent religious transformation of the region. The former Sasanid provinces, in alliance with Parthian and White Hun nobles, resisted for about a century in Tabaristan, the region south of the Caspian Sea, even as the Rashidun Caliphate was replaced by the Umayyads, thus perpetuating the Sasanid court styles, Zoroastrian religion, and Persian language.
Text from the Wikipedia article Battle of Nahavand, licensed CC BY-SA 4.0.