---
node: cleisthenes
type: person
slug: cleisthenes
title: "Cleisthenes"
lead: "Cleisthenes (active in the late 6th century BC) was the Athenian aristocrat whose reforms of 508/507 BC created the framework of Athenian democracy: ten new tribes, the deme as the unit of citizenship, a Council of Five Hundred, and the assembly at the center of decision-making. He is often called the father of Athenian democracy."
published: 2026-07-10
updated: 2026-07-10
---

## Who they were

Cleisthenes was an Athenian aristocrat of the Alcmaeonid family, active in the late 6th century BC. His birth and death dates are unknown — a birth around c. 570 BC is conventional — and he disappears from the record after his reforms. He is often called the father of Athenian democracy.

## What they did

After the fall of the Peisistratid tyranny in 510 BC, Cleisthenes faced a power struggle with Isagoras, who called in a Spartan king; a popular uprising restored Cleisthenes, and he carried his reforms in 508/507 BC. He created ten new tribes that deliberately mixed city, coastal, and inland demes, breaking the regional blocs of the aristocracy, and made the deme the unit of citizenship. A Council of Five Hundred — fifty per tribe — was established, and the assembly became the decision-making center. His own watchword was isonomia, equality before the law. Ostracism, the ten-year exile decided by vote, is attributed to his reforms per the Aristotelian Constitution of the Athenians, though its first known use came only in 487 BC.

## Legacy

The machinery Cleisthenes built ran Athenian democracy for nearly two centuries. It remains the classic case study of institutional design against faction.