In Ancient Greece, a deme or demos was a suburb or a subdivision of Athens and other city-states. Demes as simple subdivisions of land in the countryside existed in the 6th century BC and earlier, but did not acquire particular significance until the reforms of Cleisthenes in 508 BC. In those reforms, enrollment in the citizen-lists of a deme became the requirement for citizenship; prior to that time, citizenship had been based on membership in a phratry, or family group. At this same time, demes were established in the main city of Athens itself, where they had not previously existed; in all, at the end of Cleisthenes' reforms, Athens was divided into 139 demes. Three other demes were created subsequently: Berenikidai, Apollonieis, and Antinoeis. The establishment of demes as the fundamental units of the state weakened the gene, or aristocratic family groups, that had dominated the phratries.

The city of Athens during the classical period of ancient Greece was the major urban centre of the notable polis (city-state) of the same name, located in Attica, Greece, leading the Delian League in the Peloponnesian War against Sparta and the Peloponnesian League. Athenian democracy was established in 508 BC under Cleisthenes following the tyranny of Isagoras. This system remained remarkably stable, and with a few brief interruptions remained in place for 180 years, until 322 BC. The peak of Athenian hegemony was achieved in the 440s to 430s BC, known as the Age of Pericles.