It was the Assyrians who were the first to organize and exploit the first standing army in history. A standing army being a professional and permanent one, the Assyrians employed their army, as many as 100,000 strong according to one text, for ruthless extermination of those who opposed them. They carved out an enormous empire encompassing most of Mesopotamia. The Assyrians possessed a well-defined chain of command, with specialist units of cavalry, armed with iron-tipped spears, slingers, and bowmen, whose massed fire could be devastating to an enemy, and which led to an increased use in armor, such as knee-length scale tunics. They also developed extensive expertise in siege warfare, and in the taking of Lachish (701 BC) deployed siege engines that were not surpassed until Roman times.
The Assyrian State under kings such as Tiglath Pileser III (745–27 BC) was capable of fighting sustained campaigns and defending a large area with mobile chariot forces. In the end, however, the multinational nature of its empire was to prove its undoing, as its resources became overstretched and a series of revolts caused its rapid collapse in 612 BC. The Persians, too, built a multi-ethnic empire from the mid-6th century BC, but on a magnified scale, stretching from the borders of India to the Aegean. At the heart of their army was an elite corps of "Immortals," fighting with short spear and bow from behind a shield-wall. As the Persian domain expanded, light cavalry from Media, light infantry from the mountain regions, and even a camel-corps from the Middle East were added. Ironically, despite this well-balanced combination, the Persians were eventually defeated by an apparently tactically inflexible force, the Greek hoplite army.