The Macedonian phalanx, with its 18-foot sarissa pike, was a genuinely revolutionary military technology when Philip II introduced it in the 4th century BC. The tactical problems it solved and the problems it created shaped warfare in the Hellenistic world for two centuries.

The sarissa's length meant that a phalanx could overlap multiple ranks of pikes simultaneously: a soldier in the fifth rank could bring his sarissa to bear over the heads of the four ranks in front of him. The concentrated point pressure on any attacking formation was enormous. Against anything frontal, the sarissa phalanx was nearly impenetrable.

But the sarissa phalanx was brittle in ways that the older hoplite formation was not. The unwieldy length of the sarissa made it slow to maneuver, vulnerable on its flanks and rear, and almost useless in broken terrain. Alexander's genius was understanding that the phalanx needed companion cavalry to protect its flanks and to exploit the breakthroughs it created — the phalanx was a pinning force, not a decisive arm.

Roman legionaries were trained specifically to fight the Macedonian phalanx, and their tactics for doing so — seeking broken ground, throwing heavy javelins to destroy the pike points, fighting under the pikes once the formation closed — are documented in Livy's account of the Battle of Cynoscephalae (197 BC). The flexibility of the maniple system against the rigidity of the phalanx is one of the cleaner tactical lessons from ancient military history.