Satrap (Greek σατράπης satrápēs, from Old Persian xšaθrapā(van), i.e. "protector of the land/country"). In the ancient Persian Achaemenid and Sassanid empires, the name given to the governors of the provinces.
By the earlier Greek authors (Herodotus, Thucydides and often in Xenophon) it is rendered by satrápēs "lieutenant, governor," in the documents--from Babylonia and Egypt and in Ezra and Nehemiah by pakha, "governor"; and the satrap Mazaeus of Cilicia and Syria in the time of Darius III and Alexander (Arrian iii. 8) calls himself on his coins "Mazdai, who is [placed] over the country beyond the Euphrates and Cilicia." (Compare 'Ahura Mazda,' the 'Wise Lord' God of the Persians.)
When Cyrus the Great found himself in control of the world's first empire outside China, he adopted the organizing principle of the Assyrians, who had first organized their conquered territories into provinces, ruled by client-kings The chief difference was that in Persian culture the concept of kingship was indivisible from divinity: divine authority validated the divine right of kings. The twenty satraps established by Cyrus were not kings, but viceroys ruling in the king's name. Darius gave the satrapies a definitive organization, increased their number to twenty-three and fixed their annual tribute (Behistun inscription).
The satrap was the head of the administration of his province, and found himself surrounded by an all-but-royal court; he collected the taxes, controlled the local officials and the subject tribes and cities, and was the supreme judge of the province before whose "chair" (Nehemiah3:7) every civil and criminal case could be brought. He was responsible for the safety of the roads (cf. Xenophon), and had to put down brigands and rebels. He was assisted by a council of Persians, to which also provincials were admitted; and was controlled by a royal secretary and by emissaries of the king, especially the "eye of the king" who made an annual inspection.
There were checks on the power of the satraps: beides his secretarial scribe, his chief financial official (Old Persian ganzabara) and the general in charge of the regular army of his province and of the fortresses were independent of him and reported directly to the shah, periodically, in person. But the satrap was allowed to have troops in his own service (in later times mostly Greek mercenaries). The great provinces were divided into many smaller districts, the governors of which are also called satraps and (by Greek authors) hyparchs ('vice-regents'). The distribution of the great satrapies was changed occasionally, and often two of them were given to the same man. Whenever central authority in the empire weakened, the satrap often enjoyed practical independence, especially as it became customary to appoint him also as general-in-chief of the army district, contrary to the original rule. "When his office became hereditary, the threat to the central authority could not be ignored" (Olmstead). Rebellions of satraps became frequent from the middle of the 5th century. The great usurper Darius I struggled with widespread rebellions in the satrapies, and under Artaxerxes II occasionally the greater part of Asia Minor and Syria was in open rebellion.
The last great rebellions were put down by Artaxerxes III. The satrapic administration was retained by Alexander and his successors, especially in the Seleucid empire, where the satrap generally is designated assirategus; but their provinces were much smaller than under the Persians.
In later times the divine cult of a Satrapes occurs in Syrian inscriptions from Palmyra and the Hauran. Pausanias (vi.25, 26) mentions 'Satrapes' as the name of a god who had a statue and a cult in Elis and is identified with Korybas. The origin of this 'god' is obscure; perhaps it arose from a cult identifying the divine and royal aspect of the satrap's power.