The army of ancient Macedon is considered to be among the greatest military forces of the ancient world. It became the formidable force known from history first under the rule of King Philip II of Macedon and then his son, Alexander the Great.

The military innovations, both in weapons and tactics, brought forth by Philip II of Macedonia were what truly forged the army that conquered an empire. He turned warfare and combat into a way of life for the Macedonians, who until then had treated the military as a part-time occupation to be pursued during the off-season from farming. By introducing the military as a full-time occupation, Philip II of Macedonia was able to drill his men regularly, building unity and cohesion. This created one of the finest military machines that Asia or Greece had ever seen, thanks to the amount of time and effort spent on maneuvers as well as military innovations.

Tactical innovations included the more effective use of the traditional Greek phalanx, as well as coordinated attacks (early combined arms) and tactics between his phalanx infantry units, cavalry, archers, and siege engines. Weapons introduced included the sarissa, a type of counter-weighted long pike, which created many advantages, both offensively and defensively, for the Macedonian infantry in particular, and for its combined military in general.

The heavy cavalry included the Companion cavalry, raised from the Macedonian nobility, and the Thessalian cavalry.

The Companion cavalry (hetairoi, mounted noble 'companions'; like philoi (basilikoi) '(royal) friends', the term became an aulic title in the diadochi period) was divided into eight squadrons called ile, 200 strong, except the Royal Squadron of 300. They were equipped with a 3 meter lance, the xyston, and heavy body armor. During the reign of Alexander the Great, cavalrymen carried no shields. However, the Companion cavalry of the Antigonid dynasty did carry large, round bossed shields of Celtic origin.

The organization of the Thessalian cavalry was similar to the Companion Cavalry, but they had a shorter spear and fought in a looser formation.

Of light cavalry, the prodromoi (runners) secured the wings of the army during battle and went on reconnaissance missions. Several hundred allied horses rounded out the cavalry, but were inferior to the rest.

In battle, the Macedonian cavalry under Alexander and Philip II would hit the flanks or rear of the enemy, who would be trying to beat the phalanx of sarissa wielding pikemen in a phalanx. It seems to appear that Alexander would organize his left flank into a thin line to make it appear weak, while a massive phalanx would be on the right. The enemy would attack the left flank, and the phalanx would counter them, leaving the cavalry (behind the phalanx) to run around and attack the enemy infantry, or even the commander, as Alexander did when he defeated Darius once.

The Macedonian phalanx is an infantry formation developed by Philip II and used by his son Alexander the Great to conquer the Persian Empire and other armies. Phalanxes remained dominant on battlefields throughout the Hellenistic period, although wars had evolved into more protracted operations generally involving sieges and naval combat as much as field battles, until they were finally displaced by the Roman Legion.

Philip II spent much of his youth as a hostage at Thebes, where he studied under the renowned general Epaminondas, whose reforms were the basis for the Phillip's tactics. Phalangites were professional soldiers, and were among the first troops ever to be drilled, thereby allowing them to execute complex maneuvers well beyond the reach of most other armies. They fought packed in a close rectangular formation, typically eight men deep (becoming sixteen men deep under Phillip), with a leader at the head of each column and a secondary leader in the middle, so that the back rows could move off to the sides if more frontage was needed.

Each phalangite carried as his primary weapon a sarissa, a double-pointed pike over 6 m (18 ft) in length. It is the belief of some that these pikes were so large and heavy that they had to be wielded with two hands in battle, but this would contradict statues and reports contemporary to phalangist troops that showed these soldiers wearing large and heavy shields over one arm; regardless, it is likely that phalangite training was sufficient to permit proper use of the shield and sarissa. Before a battle the sarissa were carried in two pieces and then slid together when they were being used. At close range such large weapons were of little use, but an intact phalanx could easily keep its enemies at a distance; the weapons of the first five rows of men all projected beyond the front of the formation, so that there were more spearpoints than available targets at any given time. A phalangite also carried a secondary weapon, a short sword for close quarter fighting.

Neither Philip nor Alexander actually used the phalanx as their arm of choice, but instead used it to hold the enemy in place while their heavy cavalry broke through their ranks. The Macedonian cavalry fought in wedge formation and was stationed on the far right; after these broke through the enemy lines they were followed by the hypaspists, lighter infantrymen who served as the king's bodyguard, and then the phalanx proper. The left flank was generally covered by allied cavalry supplied by the Thessalians, which fought in rhomboid formation and served mainly in a defensive role. Other forces — skirmishers, range troops, reserves of allied hoplites, Cretan archers, and artillery — were also employed. The phalanx carried with it a fairly minimal baggage train, with only one servant for every few men. This gave it a marching speed that contemporary armies could not hope to match — on occasion forces surrendered to Alexander simply because they were not expecting him to show up for several more days. Phalangites were drilled to perform short forced marches if required.

The armies of the early Hellenistic period were equipped and fought mainly in the same style as Alexander's. Towards the end, however, there was a general slide away from the combined arms approach back to using the phalanx itself as the arm of decision, having it charge into the enemy lines much like earlier hoplites had. This left the formation fairly vulnerable — though near invincible to forwards assault, phalanxes like other infantry formations were fairly prone to flanking, and worse still tending to break up when advancing quickly over rough ground. So long as everyone was using the same tactics these weaknesses were not immediately apparent, but with the advent of the Roman legion they proved fatal in every major engagement, the most famous being the Battle of Pydna, as the Romans were able to advance through gaps in the line and easily defeat the Phalangites once in close.

The Macedonian phalanx was not very different from the Hoplite phalanx of other Greeks states, save it was better trained, armed with the pike enabling it to outreach its competitors and stave off enemy cavalry, and wore far lighter armor enabling longer endurance and long fast forced marches, including the ability to sprint to close and overwhelm opposing positions and archers. In essence, the range of their counter-weighted sarissa pike, allowed them superior mobility as well as superior defense and attack abilities despite the encumbrance disadvantages of the longer weapon once trained up to handling it in formation. Centuries later, the Canton organized militia of Swiss Pikemen enjoyed similar advantages over less well trained contemporary militaries which were identically equipped, which emphasizes the importance of training and unit cohesion in the scheme. In Phillip's and Alexander's time, the Macedonian phalanx had clear technical superiority.

The cavalry would mostly be positioned on a wing of the army and normally would wait for the Phalanx to lock the enemy in place before charging the flank or rear, often to devastating effect as very few enemies would deviate from the combat - a Greek phalanx would have physical difficulty and most opponents would be killed as they marched perpendicular to the line, then the now-free wing group would attack the main army's flank and begin an envelopment maneuver. This was not always used, however, at the Hydaspes River the cavalry moved far off to the left wing with a few pikemen and ambushed the Indians. At Gaugamela the cavalry moved straight for the Persian King and the hypaspists covered the flanks with the support of javelin skirmishers and allied cavalry. These proved important when the right wing cavalry hit the left guard under Parmenion, forcing the companions to pull back from their pursuit of the Persian left.

• Hellenistic armies
• Hoplite
• Pezhetairoi
• Companion cavalry
• Phalanx
• Sarissa
• Xyston
• Battle of Chaeronea (338 BC)
• Battle of Granicus
• Battle of Issos
• Battle of Gaugamela
• Battle of Hydaspes
• Siege of Tyre
• Battle of Pydna
• Battle of Cynoscephalae
• Aelianus Tacticus

• The Seventy Great Battles of All Time, Edited by Jeremy Black, Thames & Hudson Ltd, 2005

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