Tactical formation consisting of a block of heavily armed infantry standing shoulder to shoulder in files several ranks deep. First used by the Sumerians and fully developed by the ancient Greeks, it is viewed today as the beginning of European military development. The Greek city-states adopted a phalanx eight men deep during the 7th century BC. The spectacle of Greek hoplites marching forward in solid ranks was frightening to the enemy, but the phalanx was difficult to maneuver and easily thrown into confusion if its ranks were broken.
Learn more about phalanx with a free trial on Britannica.com.