The Persians most likely used their bows to wear down the enemy, then closed in to deliver the final blow with spears and swords. The first rank of Persian infantry formations, the so-called 'sparabara', had no bows, carried larger wicker shields and were sometimes armed with longer spears. Their role was to protect the back ranks of the formation. The cavalry probably fought as lightly armed missile cavalry. The style of warfare between the Greek city-states, which dates back until at least 650 BC (as dated by the 'Chigi vase'), was based around the hoplite phalanx supported by missile troops. The 'hoplites' were foot soldiers usually drawn from the members of the middle-classes (in Athens called the "zeugites"), who could afford the equipment necessary to fight in this manner. The heavy armour usually included a breastplate or a linothorax, greaves, a helmet, and a large round, concave shield (the "aspis or hoplon"). Hoplites were armed with long spears (the "dory"), which were significantly longer than Persian spears, and a sword (the "xiphos"). The heavy armour and longer spears made them superior in hand-to-hand combat and gave them significant protection against ranged attacks. Lightly armed skirmishers, the psiloi also comprised a part of Greek armies growing in importance during the conflict; at the Battle of Plataea, for instance, they may have formed over half the Greek army. Use of cavalry in Greek armies is not reported in the battles of the Greco-Persian Wars. At the beginning of the conflict, all naval forces in the eastern Mediterranean had switched to the trireme, a warship powered by three banks of oars. The most common naval tactics during the period were ramming (Greek triremes were equipped with a cast-bronze ram at the bows), or boarding by ship-borne marines. More experienced naval powers had by this time also begun to use a manoeuver known as "diekplous". It is not clear what this was, but it probably involved sailing into gaps between enemy ships and then ramming them in the side. The Persian naval forces were primarily provided by the seafaring people of the empire: Phoenicians, Egyptians, Cilicians and Cypriots. Other coastal regions of the Persian Empire would contribute ships throughout the course of the wars. In 507 BC, Artaphernes, as brother of Darius I and Satrap of Asia Minor in his capital Sardis, received an embassy from newly democratic Athens, probably sent by Cleisthenes, which was looking for Persian assistance in order to resist the threats from Sparta.