The Macedonian phalanx 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, the phalanx appeared obsolete against the more manoeuvrable Roman legions.

Infantry is a specialization of military personnel who engage in warfare combat. Infantry generally consists of light infantry, irregular infantry, heavy infantry, mountain infantry, motorized infantry, mechanized infantry, airborne infantry, air assault infantry, and naval infantry. Other types of infantry, such as line infantry and mounted infantry, were once commonplace but fell out of favor in the 1800s with the invention of more accurate and powerful weapons.