Philip, when a hostage in Thebes, the city of Epaminondas, had learnt to appreciate the strength and weakness of trained mer cenaries; their discipline was magnificent but they were lacking in patriotism. On his return to his kingdom, he determined to model his troops on what was then a new idea, namely, a highly trained and disciplined standing army. This force being patriotic and disciplined would possess both the virtue of the old militia man and the skill of the trained mercenary. As he already pos sessed the best cavalry in Greece, if he could now raise an effi cient force of infantry, and combine these two arms scientifically, he would create for himself an instrument more powerful than that of any city or state in Greece. The system he worked on is not fully known, but much of it can be discovered from an anal ysis of the army commanded by his son, for it was only towards the close of Alexander's reign that changes in Philip's organization were made. First Philip took the Spartan phalanx as his model, but in place of looking upon it as an offensive force, he organized it as a stable base from which offensive action could be developed by his cavalry. This protective base he armed with a pike called the sarissa, which was in length double, or nearly double, that of the Spartan weapon, which at this time was about milt. long. This lengthening of the pike may be compared to increasing the range of a modern rifle, for it meant that the enemy armed with the short pike would be outranged. It is true that the sarissa was a clumsy offensive weapon, but, as far as can be gathered, Philip never intended it as such; what, apparently, he aimed at was the establishment on the battlefield of an impenetrable wall of spikes, a mobile fortress upon which his cavalry could pivot and manoeuvre. This protective tactical base was organized into six divisions, each consisting of about 5,000 men. Each of these men, as in the Spartan phalanx, was allowed one or more servants who were lightly armed and could be employed for forays, raids and operations in hilly country.
To the phalanx Philip attached two cavalry wings, mobile arms which could hit out from it ; the right wing was in idea offensive, and the left defensive. The main strength of the right lay in the Macedonian cavalry—the Companions—and of the left in the Thessalian cavalry, the second best cavalry in the army. As both these forces of cavalry were mainly for shock action, Philip added to each wing bodies of light cavalry; normally, the Saris sophori, or Lancers, and the Paeonians were allotted to the right wing, and the Odryssian cavalry to the left. Between the cavalry of the right wing and the right of the phalanx Philip inserted a "joint" of highly trained and armoured infantry known as the Hypaspists, of which a picked body constituted the Agema, or Royal Foot Guards, just as a selected regiment of the Companion cavalry, the cavalry Agema, were the Royal Horse Guards. This armoured infantry carried the short pike and were not protective troops like those of the phalanx, the Pezetaeri, but mobile of fensive troops which normally, when the cavalry of the right wing charged forward, simultaneously protected the cavalry's left flank and the right flank of the phalanx. Should the charge of the heavy cavalry succeed, the Hypaspists, under cover of the cav alry on their right flank and the phalanx on their left, could take advantage of the enemy's disorder and work into his shattered front. The only point of weakness remaining was the right, or outer, flank of the right wing cavalry, which Philip protected by a body of skilled light infantry, the Agrianians, archers and the Thracian javelin-men.
A comparison between the Macedonian organizations and those of the Spartans and, later on, the Thebans under Epaminondas, shows clearly the genius of Philip. In the Spartan phalanx tactics were little more than push of pike, in which drill and courage generally won the day. In Epaminondas's battle order is seen clearly the idea of concentration of force against a weak point, but the blow is still delivered by infantry and is consequently slow, the Theban cavalry being no more than a protective force to the decisive infantry attack. In Philip's order organization is scientific. First, the moral element is not only based on discipline but on patriotism; secondly, the protective element is fully de veloped in the armoured and sarissa-armed Pezetaeri and the light infantry; thirdly, the offensive element is represented by the Hypaspists; and fourthly, the mobile element by the cavalry.