A Persian society has its origins in the sixth century B.C.E. with the rise of the dynasty of the Achaemenids during 558 B.C.E. under Cyrus the Great. Later rulers such as Cambyses, Darius, and Xerxes would create the largest, most stable, and in many ways most tolerant empire of its age. The Persian political, social, and religious influences would transcend the centuries. Eventually the Achaemenids would be followed by the Seleucids (323–83 B.C.E.), the Parthians (247 B.C.E.–224 C.E.), and finally the Sassanids (224–651 C.E.). When the Sasanids were defeated by Islamic invaders in 651 a new age in Persian history dawned.
Two related Indo-European tribes, the Persians and Medes, migrated into Persia in the centuries before 1000 B.C.E. Although these tribes originally had limited political organization, they were great horsemen and militarily powerful. Expansion began under the Achaemenids during the reign of Cyrus, known both for his brilliance at military strategy and his enlightened and tolerant view of empire. Areas such as Media, Lydia, Bactria, and Babylonia fell to Cyrus. Later Cambyses would add Egypt, and Darius, the greatest of all Persian kings, would extend the empire in the east into northern India and in the west into Thrace and Macedonia. The Achaemenids used an efficient bureaucracy and an elaborate spy network to maintain order. The empire reached its peak under Darius, who made use of regularized tax levies, centralized coinage, and an elaborate law code. The Persian Royal Road was the centerpiece of an expansive road system that allowed for easy communication. The Achaemenid state began to decline under Xerxes, who displayed little of the toleration of his predecessors such as Cyrus or Darius.
The Persian Wars with Greece, while hardly a devastating defeat for the huge Persian empire, marked an end to the period of expansion. Alexander of Macedon’s invasion in 334 B.C.E. brought about the end of Achaemenid rule. Alexander claimed the Persian kingship and hence a continuation of power, but his early death prevented any true lasting unification. The empire fell to pieces. Seleucus, one of Alexander’s generals, started the Seleucid state, which included most of the old Achaemenid empire. The Seleucids eventually fell to the Romans in 83 B.C.E. Earlier than this, however, the Seleucids had lost Iran to the Parthians and their most powerful king, Mithradates I. The Parthian state, centered around Ctesiphon, lasted until their conquest by the Sassanids in 224 C.E. Claiming to be the true heirs of the Achaemenids, the Sassanids would reach their peak under Shapur I. For a time the Sassanids stood as serious rivals to the later Romans. Arabic warriors would bring about the end of the Sassanid dynasty in 651 C.E.
The demands of empire had forced the Achaemenids to leave behind the simple political and social structures of their early nomadic past. To run an empire the size of the Persian state it was necessary to create a class of educated bureaucrats, including tax collectors, record keepers, and translators. A complex society of both free citizens and slaves developed. The formation of such a huge unified empire was a tremendous boost to trade. A rich trade network carried goods through the Persian empires from India, Mesopotamia, Iran, Anatolia, Phoenicia, Arabia, Greece, Ethiopia, and Egypt.
In addition to items such as grain, textiles, spices, gold, and ivory, religious concepts were also traded back and forth across the Persian empires. In their early stages the Persians worshipped nature gods and performed ceremonies similar to those of their Indo-European cousins in India, the Aryans. A profound change occurred through the philosophies of the seventh-century thinker Zarathustra. His philosophy was preserved by priests, known as magi, through the Avestas and Gathas. Zarathustra saw the universe and the human soul as a battleground between Ahura Mazda, who represented good and truth, and Angra Mainyu, who stood for evil and deception. This philosophy emphasized the significance of every individual’s choice because there would be a final judgment. Zarathustra did not tell his followers to renounce the world, but instead viewed the world as a material blessing from Ahura Mazda. Zoroastrianism eventually became the main religion of the Achaemenids but mainly spread throughout the empire on its own merits. The Sassanids would later use Zoroastrianism as a means of emphasizing their connection to the earlier Achaemenids. Although worship of Zoroastrianism declined after the Islamic invasion in the seventh century C.E., the main philosophies of Zarathustra have outlasted the centuries to influence Judaism, Christianity, and Islam.