the Parthian Empire During an apparent transitional period, corresponding to the reigns of Vādfradād II and another uncertain king, no titles of authority appeared on the reverse of their coins. The earlier title prtrk' zy alhaya (Frataraka) had disappeared. Under Dārēv I however, the new title of mlk, or king, appeared, sometimes with the mention of prs (Persis), suggesting that the kings of Persis had become independent rulers. When the Parthian Arsacid king Mithridates I (ca. 171-138 BC) took control of Persis, he left the Persian dynasts in office, known as the Kings of Persis, and they were allowed to continue minting coins with the title of mlk ("King"). Sasanian Empire Babak was the ruler of a small town called Kheir. Babak's efforts in gaining local power at the time escaped the attention of Artabanus IV, the Arsacid Emperor of the time. Babak and his eldest son Shapur managed to expand their power over all of Persis. The subsequent events are unclear, due to the sketchy nature of the sources. It is however certain that following the death of Babak around 220, Ardashir who at the time was the governor of Darabgird, got involved in a power struggle of his own with his elder brother Shapur. The sources tell us that in 222, Shapur was killed when the roof of a building collapsed on him. Ardaxšir (Artaxerxes) V, defeated the last legitimate Parthian king, Artabanos V in AD 224, and was crowned at Ctesiphon as Ardaxšir I (Ardashir I), šāhanšāh ī Ērān, becoming the first king of the new Sasanian Empire. At this point, Ardashir moved his capital further to the south of Persis and founded a capital at Ardashir-Khwarrah (formerly Gur, modern day Firouzabad). After establishing his rule over Persis, Ardashir I rapidly extended the territory of his Sassanid Persian Empire, demanding fealty from the local princes of Fars, and gaining control over the neighboring provinces of Kerman, Isfahan, Susiana, and Mesene. Artabanus marched a second time against Ardashir I in 224. Their armies clashed at Hormizdegan, where Artabanus IV was killed. Ardashir was crowned in 226 at Ctesiphon as the sole ruler of Persia, bringing the 400-year-old Parthian Empire to an end, and starting the virtually equally long rule of the Sassanian Empire, over an even larger territory, once again making Persia a leading power in the known world, only this time along with its arch-rival and successor