Muslim conquest of Northern Persia

Sassanian rule came to an end when the last Sassanian ruler, Yazdegerd III (632–651) was killed not far from the city and the Sassanian military governor surrendered to the approaching Arab army. The city was occupied by lieutenants of the caliph Umar and his successors where the conquest was including Tabaristan, Azerbaijan and Armenia. in later era it became the capital of the Umayyad province of Khorasan.

Aftermath
In 671, Ziyad ibn Abi Sufyan sent 50,000 Arab troops to Merv as a colony. This colony retained its native Kufan sympathies and became the nucleus of Khurasan. Using this city as their base, the Arabs, led by Qutayba ibn Muslim, brought under subjection large parts of Central Asia, including Balkh, Bokhara, and Fergana.

Legacy
Merv, and Khorasan in general was to become one of the first parts of the Persian-speaking world to become majority-Muslim. Arab immigration to the area was substantial. A Chinese captured at Talas, Du Huan, was brought to Baghdad and toured the caliphate. He observed that in Merv, Khurasan, Arabs and Persians lived in mixed concentrations.