Ardashir I, founder of the Sassanid dynasty, ruler of Siraz, born in the late 2 nd centuryin Shiraz, According to one tradition, he inherited the throne of Shiraz from his father Babak and Sasan was the name of his grandfather.The dynasty Ardashir founded would rule for four centuries until overthrown by the Rashidun Caliphate in 651. The Sassanid state as established by Ardashir I was characterized by two general trends which differentiated it from its Parthian predecessor: a strong political centralization and organized state sponsorship of #### Zoroastrianism. The Parthian Empire had consisted of a loose federation of vassal kingdoms under the suzerainty of the Arsacid monarchs. In contrast, Ardashir I established a relatively strong central government by which to rule his dominions. The empire was divided into cantons, the dimensions of which were based on military considerations. These cantons were designed to resist the influence of hereditary interests and feudal rivalries. In the latter years of his reign, Ardashir I engaged in a series of armed conflicts with Persia's great rival to the west – the Roman Empire. In 230 Ardashir I led his army into the Roman province of Mesopotamia, unsuccessfully besieging the fortress town of Nisibis. At the same time, his cavalry ranged far enough past the Roman border to threaten Syria and Cappadocia. Ardashir I campaigned unsuccessfully against Roman border outposts again the following year (231). As a result, the Roman emperor Alexander Severus (222–235) moved to the east, establishing his headquarters at Antioch, but experienced difficulties in bringing his troops together and thus made another attempt at diplomacy, which Ardashir I rebuffed. Ardashir I was an energetic king, responsible for the resurgence not just of Persia but of Iranian-speaking peoples as a unified nation, the strengthening of Zoroastrianism, and the establishment of a dynasty that would endure for four centuries. While his campaigns against Rome met with only limited success, he achieved more against them than the Parthians had done in many decades and prepared the way for the substantial successes his son and successor Shapur I would enjoy against the same enemy.