Hoplites date back to the wars between the Greek city-states in the 8th and 7th centuries BC. During the Greco-Persian Wars most hoplites wore a Corinthian-style bronze helm, and a cuirass of bronze or stiffened linen or canvas. They were armed with a short sword and an iron-tipped spear with a bronze counterbalance butt-spike. Hoplites were named, though, after the round hoplon shield they carried. The hoplon-and-spear combination required them to fight as a phalanx, a block of spearmen some eight ranks deep. When closed up, each man would find shelter behind the shield of his neighbour, creating a wall of bristling spear-points. While all hoplites were originally citizen-soldiers, full-time mercenaries took over and became the standard fighting unit of the Greek world. Later, under Phillip II of Macedon and Alexander the Great, the shield became smaller, while the spear developed into the five metre sarissa pike. Many armies adopted the phalanx of hoplites as a tactical unit because it was very successful in battle.