The Kingdom of Macedon possessed one of the greatest armies in the ancient world. It is reputed for the speed and efficiency with which it emerged from Greece to conquer large swathes of territory stretching from Egypt in the west to India in the east. Initially of little account in the Greek world, it was widely regarded as a second-rate power before being made formidable by Philip II, whose son and successor Alexander the Great conquered the Achaemenid Empire in just over a decade's time.
The latest innovations in weapons and tactics were adopted and refined by Philip, and he created a uniquely flexible and effective army. By introducing military service as a full-time occupation, Philip was able to drill his men regularly, ensuring unity and cohesion in his ranks. In a remarkably short time, this led to the development of one of what was among the world's finest military machines for the era. Tactical improvements included the latest developments in the deployment of the traditional Greek phalanx made by men like Epaminondas of Thebes and Iphicrates of Athens. Philip improved on these military innovators by using both Epaminondas' deeper phalanx and Iphicrates' combination of a longer spear and a smaller and lighter shield. However, the Macedonian king also innovated; he introduced the use of a much longer spear, the two-handed pike. The Macedonian pike, also known as the sarissa, gave its wielder many advantages both offensively and defensively. For the first time in Greek warfare, cavalry became a decisive arm in battle. The Macedonian army perfected the co-ordination of different troop types in an early example of combined arms tactics—the heavy infantry phalanx, skirmish infantry, archers, light cavalry and heavy cavalry, and siege engines were all deployed in battle; each troop type being used to its own particular advantage and creating a synergy of mutual support.
