Cleisthenes of Athens

Cleisthenes reorganized the Athenian citizen body into ten new tribes based on demes (local districts), replacing the old four Ionian tribes. This broke the power of aristocratic clans and created a new political structure that formed the basis of Athenian democracy.

Cleisthenes introduced the practice of ostracism, allowing citizens to vote annually to exile a prominent figure for ten years. This mechanism was designed to prevent tyranny and remove threats to democracy. The first ostracism occurred in 487 BC.

Cleisthenes established the Boule, a council of 500 citizens (50 from each tribe) chosen by lot. This body prepared legislation for the Assembly and oversaw daily administration. It replaced the aristocratic Areopagus as the main governing body, expanding citizen participation.

Cleisthenes' rival Isagoras called on Spartan king Cleomenes I to intervene in Athens. The Spartans expelled Cleisthenes and attempted to dissolve the Boule, but the Athenian people revolted, besieging the Acropolis and forcing the Spartans to withdraw. Cleisthenes was recalled.