There was deep need of skill, as well as of valour, on Alexander's side; and few battle-fields have witnessed more consummate generalship than was now displayed by the Macedonian king. There were no natural barriers by which he could protect his flanks; and not only was he certain to be overlapped on either wing by the vast lines of the Persian army, but there was imminent risk of their circling round him and charging him in the rear, while he advanced against their centre. He formed, therefore, a second or reserve line, which was to wheel round, if required, or to detach troops to either flank; as the enemy's movements might necessitate: and thus, with their whole army ready at any moment to be thrown into one vast hollow square, the Macedonians advanced in two lines against the enemy, Alexander himself leading on the right wing, and the renowned phalanx forming the centre, while Parmenio commanded on the left. Such was the general nature of the disposition which Alexander made of his army. But we have in Arrian the details of the position of each brigade and regiment; and as we know that these details were taken from the journals of Macedonian generals, it is interesting to examine them, and to read the names and stations of King Alexander's generals and colonels in this the greatest of his battles. The eight troops of the royal horse-guards formed the right of Alexander's line. Their captains were Cleitus (whose regiment was on the extreme right, the post of peculiar danger), Graucias, Ariston, Sopolis, Heracleides, Demetrias, Meleager, and Hegelochus. Philotas was general of the whole division. Then came the shield-bearing infantry: Nicanor was their general. Then came the phalanx, in six brigades. Coenus's brigade was on the right, and nearest to the shield-bearers; next to this stood the brigade of Perdiccas, then Meleager's, then Polysperchon's; and then the brigade of Amynias, but which was now commanded by Simmias, as Amynias had been sent to Macedonia to levy recruits. Then came the infantry of the left wing, under the command of Craterus. Next to Craterus's infantry were placed the cavalry regiments of the allies, with Eriguius for their general. The Messalian cavalry, commanded by Philippus, were next, and held the extreme left of the whole army. The whole left wing was entrusted to the command of Parmenio, who had round his person the Pharsalian troop of cavalry, which was the strongest and best amid all the Thessalian horse-regiments.