Greek mercenaries were professional warriors who were superior in martial arts to the warriors of the rest of the world, which created a demand for their use in other countries. This book presents the history of the transformation of an army of "amateur" soldiers from their initial primitive state in ancient times (7th century BC) into a developed organized force in the Hellenistic era. Mercenaries recruited from ethnic Greeks were recruited into the service of the states of the Mediterranean and the Middle East and played a significant role not only in military expeditions, but also in the social and political history of the eras of Cyrus the Younger, Dionysius I, Philip II and other tyrants and autocrats. It was they who contributed to the formation and defense of the empire of Alexander the Great. But their predominance in the army was a passing period in Greek history. The professional soldiers of Greece themselves changed over time, and later their military qualities ceased to correspond to the developing art of war.