Assessment of Greek land warfare must also reckon with currently popular 'face-of-battle' studies. Viewed positively, the 'face-of-battle' approach has revived attention to the role of morale in battle and the details of small unit combat. For some a phalanx can be found in Homer and the introduction of hoplite armour did not 'revolutionize' warfare. The Persian Wars and fifth-century Athenian imperialism would call the agonal system into question and begin teaching the art of generalship. Naval and siege warfare played central roles in classical Greece, but they were much simpler, inexpensive and less lethal before c. 500 BC. Siege warfare was little known in the Greek mainland before that time; naval warfare was more common but still relatively undeveloped. New developments in these two spheres tended to begin at the eastern and western fringes of the Greek world, as a result of contact with foreign peoples, and then to make their way dramatically to centre stage on the Greek mainland.