ALEXANDER’S GENERALSHIP AT THE BATTLES OF THE RIVER GRANICUS (334), ISSUS (333), AND GAUGAMELA (331)
The assassination of Philip in summer 336 postponed the invasion of the Persian Empire for two years. When Alexander ascended to the Macedonian throne, he was immediately threatened by enemies on all sides. His first immediate task was to remove all potential challengers for the kingship which he did with alacrity (Plutarch Moralia 327). His second was to establish himself in his father’s place as commander-in-chief of the Greeks for the planned military campaign against Persia: his swift march through Greece resulted in his election to this post by the League of Corinth (Diodorus 17.3-4). Alexander’s third task was to ensure that Macedon was safe from an attack by the traditionally hostile Illyrians on its western border, and that there was no danger of a Thracian revolt in his rear, while waging war in Asia: his successful campaigns in 335 against the Triballi, the most rebellious of the Thracian tribes, and against the Illyrians put an end to these problems (Arrian, Anabasis 1.1-6). In the same year the sack of Thebes after its uprising served as a warning to all the Greek states that Alexander would deal ruthlessly with any opposition (Diodorus 17.13-14). Alexander was now ready in the spring of 334 to invade the Persian Empire: he crossed the Hellespont and, before coming to land, cast his spear into the Asian soil, thus asserting his claim to Asia by right of conquest (Diodorus 17.17). His victory in three great battles at the River Granicus (334), at Issus (333) and at Gaugamela (331) turned his claim into fact.