In the ancient world, three dynasties of Persian speaking peoples created vast empires across central Asia and the Near East: the Achaemenid (559-330 BC), the Parthian (ca. 247 BC-AD 224), and the Sasanian (AD 224-651). Although each of the Persian empires shared certain cultural attributes and a fair amount of geographical space, each dynasty was also unique and important in its own way. Stretching from the Indus River in the east to the Euphrates River in the west, and from the Oxus River in the north to the Persian Gulf in the south, the Sasanian Empire was every bit as large and powerful as its two predecessors.
The Sasanians were known for following and codifying many of the Achaemenid and Parthian cultural and religious traditions, such as the rituals of the Zoroastrian religion in the collection of religious texts known as the Avesta. Like the Parthians before them, the Sasanians fought the Romans, and later the Byzantines, for control of Mesopotamia and ultimately lost a war for their very existence against the Islamic Arab armies, which signaled the beginning of Islam’s ascendancy in the region and the end of the ancient Near East.
But long before Islam overtook Persia, the Sasanians fought a war against the Parthians for control of the region. The Sasanians achieved their victory through a combination of superior leaders, tactics, and organization and despite the violent overthrow of the Parthian Dynasty, the transition from Parthian to Sasanian rule was incredibly seamless. The early Sasanian kings pursued a program of continuity with the Parthian and Achaemenid dynasties in their use and acceptance of religion, language, and history, which ultimately made the dynasty strong enough to resist outside forces.