The Mercenary is one who doesn't fight for king, for country, or for glory. The Mercenary fights for wealth. Mercenaries have been utilized for almost as long as civilization itself. The ancient Egyptians have the first properly recorded use of mercenaries in the Nubians. The Nubians lived south of Egypt, in sub-Saharan Africa. They were darker skinned than the Egyptians, wore different clothes, and worshiped different gods. At first. The Egyptians hired the Nubians because of their skill with a bow, at the time one of the most advanced weapons of war. The Egyptians hired so many Nubian mercenaries that Nubian culture began to permeate throughout Egypt. Egyptian culture remained dominant, but it was forever changed by the mercenaries.
One would think in a time of empires and in a time before large scale Mercantilism or Capitalism that mercenaries would be much more rare, used only as a last resort. Surprisingly, however this was one of the best times to be a mercenary, rivaling even the modern day. Greece, Phoenicia, the Persians, practically every of the classical Mediterranean cultures used mercenaries. The most popular of these were the Celts. Celtic mercenaries were hired by the tribe for their skill, strength, stupid levels of bravery, and shocking brutality. They saw action all across the Mediterranean and often fought one and other, as they had been hired by opposing sides. They did have problems following orders, and retreat wasn't in their vocabulary, but they were still paid handsomely for their services, primarily in plunder, but occasionally in land. The biggest being the Galacian settlement in modern day Spain, which many believe was given to Celtic mercenaries for services rendered to the Phoenicians.