The ancient military formation used by the Greeks in battle was the phalanx. This formation involved soldiers, known as hoplites, standing closely together in ranks, often eight to sixteen men deep, with shields overlapping and spears protruding forward. The phalanx allowed for coordinated and organized maneuvers, providing a unified front that was difficult for enemies to penetrate. Its effectiveness in battle was evident in various engagements, such as the battles of Marathon and Salamis. The phalanx represented a key element of Greek military strategy and contributed to the dominance of city-states like Athens and Sparta in ancient warfare.