Colonies in antiquity were post-Iron Age city-states founded from a mother-city (its "metropolis"), not from a territory-at-large. Bonds between a colony and its metropolis remained often close, and took specific forms during the period of classical antiquity. Generally, colonies founded by the ancient Phoenicians, Carthage, Rome, Alexander the Great and his successors remained tied to their metropolis, but Greek colonies of the Archaic and Classical eras were sovereign and self-governing from their inception. While Greek colonies were often founded to solve social unrest in the mother-city, by expelling a part of the population, Hellenistic, Roman, Carthaginian, and Han Chinese colonies were used for trade, expansion and empire-building.