The Macedonian phalanx (Greek: Μακεδονική φάλαγξ) is an infantry formation developed by Philip II and used by his son Alexander the Great to conquer the Achaemenid Empire and defeat armies of other kingdoms. Phalanxes remained dominant on battlefields throughout the Hellenistic period, although wars had developed into more protracted operations generally involving sieges and naval combat as much as pitched battles, until they were ultimately displaced by the Roman legions.