Among the provinces of the Sāsānian empire, the coastal regions along the southern shore of the Caspian Sea resisted the penetration of the Arabs and Islam most tenaciously. The early history of the Sāsānian dynasty is, however, shrouded in obscurity. The first mention of an Ispahbad ruling Tabaristān in a reliable report concerns the year 79/698. Tabaristān was ruled by Muslim governors residing in Āmul. Their first task was to secure the Muslim domination over the newly subdued territories. Though the nobility was generally left unharmed, some prominent Zoroastrian leaders were killed during the first years of the occupation. The history of the Bāvandid, Ispahbads of Shahriyārkūh in the 4th/ioth century can only fragmentarily be pieced together from occasional references in literary sources and some numismatic evidence. Rūyān in the 4th/10th century came under the rule of a dynasty bearing the title Ustandār. The population of Azarbaijan at the time of the conquest was predominantly Iranian, speaking numerous dialects.