Ancient Greece was a loose collection of Greek-speaking city-states centered on the Aegean Sea. The most famous of these city-states was Athens, because it was the center of the Athenian Empire (called the Delian League), and because it bred such keen minds and great artists as the philosopher Socrates, the historian Thucydides, and the playwright/poet Sophocles. Ancient Greece, and especially Athens, is credited with a host of innovations, so that it has often been described as the (or a) cradle of Western civilization. Democracy, in one form, arose there, and popularized especially by the great Athenian statesman Pericles. Philosophy, natural science, historiography, the theater, realism in the arts, and many other disciplines and arts had their origin in ancient Greece.