The Macedonian phalanx (Greek: Μακεδονική φάλαγξ) was an infantry formation developed by Philip II from the classical Greek phalanx, of which the main innovation was the use of the sarissa, a 6-metre pike. It was famously commanded by Philip's son Alexander the Great during his conquest of the Achaemenid Empire between 334 and 323 BC. The Macedonian phalanx model then spread throughout the Hellenistic world, where it became the standard battle formation for pitched battles. During the Macedonian Wars against the Roman Republic (214–148 BC), the phalanx appeared obsolete against the more manoeuvrable Roman legions.