The ancient army known for its use of phalanx formation was the Macedonian army, particularly under King Philip II and his son, Alexander the Great. The phalanx was a tactical formation that grouped soldiers into densely packed lines, armed with long spears called sarissas and shields, providing both offense and defense. This innovative military strategy allowed the Macedonian army to achieve remarkable victories against larger enemies and become one of the most formidable military forces of the ancient world. The phalanx formation influenced subsequent military tactics and showcased the effectiveness of discipline and organization in warfare.