However, all of Iran was still not under Arab control, and the region of Daylam was under the control of the Daylamites, while Tabaristan was under Dabuyid and Paduspanid control, and the Mount Damavand region under Masmughans of Damavand. The Arabs had invaded these regions several times, but achieved no decisive result because of the inaccessible terrain of the regions. The most prominent ruler of the Dabuyids, known as Farrukhan the Great (r. 712-728), managed to hold his domains during his long struggle against the Arab general Yazid ibn al-Muhallab, who was defeated by a combined Dailamite-Dabuyid army, and was forced to retreat from Tabaristan.