The decades that followed became known as the Golden Age of Athenian democracy, during which time Athens became the leading city of Ancient Greece, with its cultural achievements laying the foundations for Western civilization. The playwrights Aeschylus, Sophocles and Euripides flourished in Athens during this time, as did the historians Herodotus and Thucydides, the physician Hippocrates, and the philosopher Socrates. Guided by Pericles, who promoted the arts and fostered democracy, Athens embarked on an ambitious building program that saw the construction of the Acropolis of Athens (including the Parthenon), as well as empire-building via the Delian League. Originally intended as an association of Greek city-states to continue the fight against the Persians, the league soon turned into a vehicle for Athens's own imperial ambitions. The resulting tensions brought about the Peloponnesian War (431–404 BC), in which Athens was defeated by its rival Sparta.