had now under prince Ardashir I begun to conquer the neighboring regions and more far territories, such as Kirman. At first, Ardashir I's activities did not alarm Artabanus, until later, when the Arsacid king finally chose to confront him. According to al-Tabari, whose work was probably based on Sasanian sources, Ardashir I and Artabanus agreed to meet in Hormozdgan at the end of the month of Mihr (April). Nonetheless, Ardashir I went to the place before due time to occupy an advantageous spot on the plain. There he dug out a ditch to defend himself and his forces. He also took over a spring at the place. Ardashir I's forces numbered 10,000 cavalry, with some of them wearing flexible chain armor akin to that of the Romans. Artabanus led a greater number of soldiers, who, however, were less disposed, due to wearing the inconvenient lamellar armor. Ardashir I's son and heir, Shapur I, as portrayed in the Sasanian rock reliefs, also took part in the battle. The battle was fought on 28 April 224, with Artabanus being defeated and killed, marking the end of the Arsacid era and the start of 427 years of Sasanian rule. Aftermath The chief secretary of Artabanus, Dad-windad, was afterwards executed by Ardashir I. Thenceforth, Ardashir I assumed the title of shahanshah ("King of Kings") and started the conquest of an area which would be called Iranshahr (Ērānshahr). He celebrated his victory by having two rock reliefs sculptured at the Sasanian royal city of Ardashir-Khwarrah (present-day Firuzabad) in his homeland, Pars. The first relief portrays three scenes of personal fighting; starting from the left, a Persian aristocrat seizing a Parthian soldier; Shapur impaling the Parthian minister Dad-windad with his lance; and Ardashir I ousting Artabanus IV. The second relief, conceivably intended to portray the aftermath of the battle, displays the triumphant Ardashir I being given the badge of kingship over a fire shrine from the Zoroastrian supreme god Ahura Mazda, while Shapur and two other princes are watching from behind. Vologases VI was driven out of Mesopotamia by Ardashir I's forces soon after 228. The leading Parthian noble-families (known as the Seven Great Houses of Iran) continued to hold power in Iran, now with the Sasanians as their new overlords. The early Sasanian army (spah) was identical to the Parthian one. Indeed, the majority of the Sasanian cavalry were composed of the very Parthian nobles