The Greek army was one of the most organised armies in Ancient history. One of the primary reasons for its success on the battlefield was the Phalanx formation. The Greek army was dominated by the hoplite which formed the basis of their infantry divisions.
When engaging in battle, the phalanx would form a tight defence and advance towards the enemy. The defence would be held tight by the hoplite shields and greaves which formed a barrier on all sides of the unit. Each soldier was armed with a spear. The first rows would hold them horizontally toward the enemy while the rows further back would hold them vertically. The formation would be protected on the flanks by lighter infantry such as archers and slingers.
The formation was integral to Greek success in Persia and the later Macedonian Empire under Phillip II and Alexander the Great. The Phalanx lasted until the age of the Roman Empire when the testudo or tortoise effectively replaced it in battle tactics. Both the phalanx and the testudo lost its strength with the rise of heavy armed cavalry in battle.