Quick questions on The conquest of the Persian empire: HSC Ancient History

In spring 334 BC Alexander crossed the Hellespont (the modern Dardanelles) from Europe into Asia Minor with a combined Macedonian and allied Greek army - ancient figures vary, but it was in the order of forty thousand infantry and cavalry, and these totals are ancient-source estimates rather than firm counts. He led the invasion under the banner of the League of Corinth as a panhellenic, Homeric war of revenge on Persia. Turning aside to Ilium (Troy), he sacrificed to Athena, honoured the Homeric dead and reportedly exchanged his armour for a sacred shield, deliberately styling himself a new Achilles. The gesture set the tone of the whole campaign: conquest dressed as heroic, avenging crusade.

Conquest was not only battles; it was the seizure of the Persian state's resources - its royal centres and treasuries, the "sinews" that funded the empire. Sardis had opened its Lydian treasury after Granicus. After Gaugamela the great administrative capitals fell in succession: Babylon surrendered (its satrap Mazaeus went over to Alexander) and Susa yielded an enormous reserve of bullion (ancient sources put it at tens of thousands of talents - figures that are illustrative of scale rather than audited). Alexander then forced the passes into Persia proper and took Persepolis, the ceremonial heart of the Achaemenid dynasty, with the largest treasure of all.

The first battle was fought at the River Granicus in north-western Asia Minor, against the assembled western satraps rather than Darius himself. The Persian commander Memnon of Rhodes had reportedly urged a scorched-earth strategy, but the satraps chose to fight, lining their cavalry along the far bank. Alexander led the Companion cavalry across in a frontal assault, won a hard cavalry melee in which he was nearly killed, and then destroyed the Greek mercenaries in Persian pay.

In November 333 BC Darius III himself marched to confront Alexander and slipped behind him, forcing battle on the narrow coastal plain at Issus in the north-eastern corner of the Mediterranean. The confined ground cancelled the Persians' greater numbers (again given in the ancient sources at wildly inflated figures). Alexander's charge with the Companions broke the Persian left and drove towards Darius, who fled the field.

The decisive battle came on 1 October 331 BC on the open plain of Gaugamela near Arbela, ground Darius had chosen and cleared so that his cavalry and scythed chariots could operate. He massed the full imperial levy - the ancient figures (hundreds of thousands, even a million) are not credible and are best treated as illustrative. Alexander advanced obliquely to his right, stretching the Persian line and drawing its cavalry out of position until a gap opened; he then wheeled the Companions in a wedge straight at Darius.