Copper was the first metal regularly exploited by humans, smelted far back into the Neolithic. For use in large tools and weapons, it was characteristically cast as a substitute for stone in ax and mace heads along with dagger blades. Yet its softness precluded much more in the way of new types of arms.
This changed dramatically with the discovery that copper could be combined effectively with arsenic or tin to produce a far harder but still ductile alloy, bronze. Not only could it be cast into the most complex shapes, but after cold-working, yielded weapons of a hardness and tensile strength rivaling those of iron, until Roman times, when tempering came to be understood. The toughness and ductility of bronze made it possible for the dagger form to be stretched to generate a true sword by the middle of the third millennium [B.C.E.] Such an instrument, by virtue of its superior reach, maneuverability, and capacity to inflict both slashing and puncture wounds, was ideal for the kind of close combat that was the specialty of the elite warrior class. Bronze also substantially increased the penetration of holdovers like the spear, arrow, and battle-ax, which, in combination with the sword, rather quickly brought forth defensive reciprocals in bronze and bronze-reinforced helmets, shields, cuirasses, and greaves, to produce a metal-clad combatant largely immune to any but similarly accessorized adversaries.
War’s appetite for bronze fed on itself further encouraging political centralization and the dominance of military elites intent upon controlling the sources of supply: Deposits of tin, in particular, were scattered and relatively difficult to extract. Literary allusions and other records from the Bronze Age make it clear that the metal and its constituents remained valued, rare, and monopolized by those in control.
Iron changed things somewhat. Anatolian armorers had experimented with the metal, probably derived from meteoric deposits, to produce blades as far back as 2500 [B.C.E.]. Iron weapons were tough and held an edge, but were subject to rapid and continuous deterioration through rust. Rather than superiority, its large-scale use was driven more by the relative abundance of ferrous deposits. Once the higher heats required for extracting terrestrial iron were mastered, it could be produced in quantities necessary to begin to provide whole armies with at least some metallic implements.
But bronze had staying power. Because it was only minimally affected by corrosion, it could be used repeatedly and for different purposes simply by melting and recasting. Iron emerged as a red-hot pasty ball that had to be worked by hammering, rather than as a liquid that could be poured into molds. Shaping remained difficult and labor-consumptive. Gradually, a better understanding of metallurgy—basically tempering and the development of steel—led to an increased reliance on ferrous-based weapons, particularly during the [European] Middle Ages.
Yet in the age named for bronze there was no question who and what ruled the battlefield. Here there were two classes of opponents: a relative few wielding and protected by bronze, and the nonmetallic masses, essentially designated victims. Although armies ranged from the low thousands up to around 20,000, battles could be and were decided by several hundred elite fighters. A combat environment in the Bronze Age typically consisted of opposing lines of archers (often supplemented by slingers and javelin throwers) exchanging desultory fire, while champions on each side sought each other out to wage what amounted to individual combat. Yet prior to and particularly after the leadership fought each other, common soldiers were subject to promiscuous killing.
— Robert L. O’Connell, Soul of the Sword, pp. 70-71