Envisioning a new world empire based on a fusion of Greek and Iranian culture and ideals, Alexander the Great of Macedon accelerated the disintegration of the Achaemenid Empire. He was first accepted as leader by the fractious Greeks in 336 B.C. and by 334 had advanced to Asia Minor, an Iranian satrapy. In quick succession he took Egypt, Babylonia, and then, over the course of two years, the heart of the Achaemenid Empire--Susa, Ecbatana, and Persepolis--the last of which he burned. Alexander married Roxana (Roshanak), the daughter of the most powerful of the Bactrian chiefs (Oxyartes, who revolted in present-day Tadzhikistan), and in 324 commanded his officers and 10,000 of his soldiers to marry Iranian women. The mass wedding, held at Susa, was a model of Alexander's desire to consummate the union of the Greek and Iranian peoples. These plans ended in 323 B.C., however, when Alexander was struck with fever and died in Babylon, leaving no heir. His empire was divided among four of his generals. Seleucus, one of these generals, who became ruler of Babylon in 312, gradually reconquered most of Iran. Under Seleucus's son, Antiochus I, many Greeks entered Iran, and Hellenistic motifs in art, architecture, and urban planning became prevalent.

Although the Seleucids faced challenges from the Ptolemies of Egypt and from the growing power of Rome, the main threat came from the province of Fars (Partha to the Greeks). Arsaces (of the seminomadic Parni tribe), whose name was used by all subsequent Parthian kings, revolted against the Seleucid governor in 247 B.C. and established a dynasty, the Arsacids, or Parthians. During the second century, the Parthians were able to extend their rule to Bactria, Babylonia, Susiana, and Media, and, under Mithradates II (123-87 B.C.), Parthian conquests stretched from India to Armenia. After the victories of Mithradates II, the Parthians began to claim descent from both the Greeks and the Achaemenids. They spoke a language similar to that of the Achaemenids, used the Pahlavi script, and established an administrative system based on Achaemenid precedents.

Meanwhile, Ardeshir, son of the priest Papak, who claimed descent from the legendary hero Sasan, had become the Parthian governor in the Achaemenid home province of Persis (Fars). In A.D. 224 he overthrew the last Parthian king and established the Sassanid dynasty, which was to last 400 years.

Data as of December 1987