 Complete the following phrase:  In the 8th or 7th century BC, Greek armies adopted the phalanx formation. The formation proved successful in defeating the Persians when employed by the Athenians at the Battle of Marathon in 490 BC during the First Greco-Persian War. The Persian archers and light troops who fought in the Battle of Marathon failed because their bows were too weak for their arrows to penetrate the wall of Greek shields that comprised the phalanx formation. The phalanx was also employed by the Greeks at the Battle of Thermopylae in 480 BC and at the Battle of Plataea in 479 BC during the 