Re-conquest of Tabaristan (Iran)
The Māzandarān Province (Tabaristan), which lies south of the Caspian Sea, was conquered during the reign of Umar, under the command of Nuaim ibn Muqarrin’s brother, Suwaid ibn Muqarrin. During Uthman’s reign it broke into revolt, and Uthman directed Saeed ibn Al Aas, the Governor General of Kufa, to suppress it. Saeed ibn Al Aas led a strong force of 80,000 warriors to Tabaristan under his personal command. The force included such eminent persons as `Abd Allah ibn `Abbas, `Abd Allah ibn `Umar and Abd-Allah ibn al-Zubayr.
The army first entered Qom, which surrendered to them and they then advanced to Tamlisa, a coastal town. It put up a stiff resistance and after a fierce battle the Muslims overpowered the city. All the men were slaughtered and the women and children were made slaves. The harsh treatment by the Muslims of the citizens of Tamlisa, struck terror into the hearts of the people of other towns and they lost the will to resist.
The army thereafter overran the Gīlān Province and other parts of Tabaristan. Even the hilly tract which had not been conquered during the caliphate of Umar was brought under Muslim rule. Having re-conquered the whole of Tabaristan, Saeed ibn Al Aas planned to march to Khorasan, but when he found that Abdullah ibn Aamir, the Governor General of Basra, was already in Khorasan, Saeed ibn Al Aas returned to Kufa.
Read more about this topic: Military Campaigns Under Caliph Uthman