Quick questions on The historical context for Alexander the Great: HSC Ancient History

The empire Alexander set out to attack was the Achaemenid Persian empire, founded by Cyrus the Great from about 550 BC and, by the fourth century, the largest the ancient Near East had yet produced. At its height it reached from Asia Minor and Egypt in the west to the Indus in the east, and it was governed through provinces called satrapies, each under a satrap answerable to the Great King, linked by royal roads and sustained by tribute and by large numbers of Greek mercenaries. When Alexander came to the throne in 336 BC the Persian king was Darius III, who had taken the throne that same year. Despite its scale, Persia was widely thought vulnerable: Xenophon's account of the march of the Ten Thousand (401 BC) had shown that a disciplined Greek force could strike deep into the empire, and this belief underpinned the whole panhellenic case for invasion.

This is the more colourful tradition, descending largely from Cleitarchus, a writer of about the late fourth century BC whose vivid and sensational account was widely read but often unreliable. It survives through Diodorus Siculus (Book 17 of his Bibliotheke, mid first century BC), the Latin history of Quintus Curtius Rufus (first century AD), and the epitome by Justin of the Philippic Histories of Pompeius Trogus. The vulgate is rich in drama, rhetoric and moralising, and useful for episodes the soberer tradition omits, but weak on precise military and chronological detail.

Part of Plutarch's Parallel Lives (paired with Julius Caesar), this biography is anecdotal and moralising rather than a continuous history. It preserves valuable material from now-lost writers, but was written some four centuries after Alexander and selects for character and morality rather than strict accuracy.