Geographical Extent of Ancient Persia
The extent of Persia varied, but at its height, it extended southwards to the Persian Gulf and Indian Ocean; to the east and northeast, the Indus and Oxus rivers; to the north, the Caspian Sea and Mt. Caucasus; and to the west, the Euphrates River. This territory includes desert, mountains, valleys, and pastures. At the time of the ancient Persian Wars, the Ionian Greeks and Egypt were under Persian dominion.
The Ancient Persians (modern Iran) are more familiar to us than the other empire builders of Mesopotamia or the Ancient Near East, the Sumerians , the Babylonians, and the Assyrians, not only because the Persians were more recent, but because they were amply described by the Greeks. Just as one man, Alexander of Macedon (Alexander the Great), ultimately wore the Persians down quickly (in about three years), so the Persian Empire rose to power quickly under the leadership of Cyrus the Great.
Western Cultural Identity and the Persian Army
We in the West are accustomed to seeing the Persians as the "them" to a Greek "us." There was no Athenian-style democracy for the Persians, but an absolute monarchy that denied the individual, common man his say in political life*. The most important part of the Persian army was a seemingly fearless elite fighting group of 10,000, who were known as "The Immortals" because when one was killed another would be promoted to take his place. Since all men were eligible for combat until age 50, manpower was not an obstacle, although to insure loyalty, the original members of this "immortal" fighting machine were Persians or Medes.
Cyrus the Great
Cyrus the Great, a religious man and adherent of Zoroastrianism, first came to power in Iran by overcoming his in-laws, the Medes (c. 550 B.C.) -- the conquest made easy by many defectors, becoming the first ruler of the Achaemenid Empire (the first of the Persian Empires). Cyrus then made peace with the Medes, and cemented the alliance by creating not just Persian, but Median sub-kings with the Persian title khshathrapavan (known as satraps) to rule the provinces. He also respected area religions. Cyrus conquered the Lydians, the Greek colonies on the Aegean coast, the Parthians, and Hyrcanians. He conquered Phrygia on the south shore of the Black Sea. Cyrus set up a fortified border along the Jaxartes River in the Steppes, and in 540 B.C., he conquered the Babylonian Empire. He established his capital in a cold area, Pasargadae (the Greeks called it Persepolis), contrary to the wishes of the Persian aristocracy. He was killed in battle in 530. The successors of Cyrus conquered Egypt, Thrace, Macedonia, and spread the Persian Empire east to the Indus River.
Seleucids, Parthians, and Sassanids
Alexander the Great put an end to the Achaemenid rulers of Persia. His successors ruled the area as the Seleucids, intermarrying with native populations and covering a large, fretful area that soon broke up into divisions. The Parthians gradually emerged as the next major Persian power ruling in the area. The Sassanids or Sassanians overcame the Parthians after a few hundred years and ruled with almost constant trouble on their eastern borders as well as to the west, where the Romans contested the territory sometimes through to the fertile area of Mesopotamia (modern Iraq), until the Muslim Arabs conquered the area.
*Cyrus may have been welcomed by the Jews of Babylonia as a liberator and the U.N. in 1971 declared a cuneiform cylinder seal of the period that described the treatment of the inhabitants of the liberated Babylonia as the first human rights document.
See: Cyrus Charter of Human Rights