What it was
Once a year the assembly asked whether an ostracism should be held. If it voted yes, a vote was taken some weeks later in which each citizen scratched a name on a potsherd. The man with the most votes left Attica for ten years.
It was not a punishment. No charge was brought, no defence was offered, no property was confiscated, and the man returned with his citizenship intact. That is what distinguishes it from exile as a penalty.
How it worked
A quorum of six thousand is reported, though whether that was six thousand votes in total or six thousand against one man is disputed in the ancient evidence itself.
Voting was by ostrakon, a broken potsherd used as scrap. Thousands have been excavated in the Agora and the Kerameikos, many bearing the names of men we know — Themistocles, Aristides, Cimon — and some carrying insults or accusations scratched alongside.
One deposit found in a well contained a large number of sherds inscribed with a single name in only a few hands, which indicates that they were prepared in advance for distribution.
Powers and limits
The stated purpose in the ancient sources is the prevention of tyranny: a way of removing a man who had become too powerful without the machinery of prosecution.
In practice it functioned as a way of resolving a deadlock between two leading politicians, and it was used against the losing side of a policy argument rather than against would-be tyrants. It fell out of use after 417 BCE, when a coordinated manoeuvre turned it against an unintended target.
How it changed
Attributed to Cleisthenes by the tradition and first attested in use in 487 BCE, which leaves a gap the sources do not explain.
The last ostracism, of Hyperbolus, was reportedly engineered by an alliance between the two men it was aimed at. The institution was not abolished; it simply stopped being used.
What the evidence supports
Thousands of inscribed ostraka survive.
Excavated in the Agora and the Kerameikos. They are among the most direct pieces of evidence for any ancient political procedure, including the handwriting of ordinary voters.
Pre-inscribed sherds were prepared for distribution.
A deposit of sherds naming one man in a small number of hands indicates organised preparation — evidence of political management of the vote.
The quorum rule is not clear.
Ancient sources differ on whether six thousand was the total needed for a valid vote or the number required against an individual. Both readings have support.
Primary sources
Aristotle, Constitution of the Athenians 22
The institution, its attribution to Cleisthenes, and its early use.
Athenian voters, Excavated ostraka Agora and Kerameikos deposits
Thousands of inscribed potsherds, including pre-prepared batches.
Plutarch, Life of Aristides 7
The story of the illiterate voter asking Aristides to write his own name — a moral anecdote, not a report.
How to read the evidence labels
- Evidence level: Documented
- Supported by a named primary text or by excavated material evidence.
- Evidence level: Probable
- Supported by strong inference that most specialists accept.
- Evidence level: Disputed
- Substantial specialist disagreement exists; competing readings are stated.
- Evidence level: Literary
- Belongs to poetic or mythological construction rather than to history.
- Evidence level: Mythological
- Belongs to shared religious or mythic tradition rather than to any single text.
- Evidence level: Unknown
- The available evidence is insufficient to decide.
These labels describe the status of the evidence, not our confidence in a conclusion. A claim marked Literary is not a claim we doubt; it is a claim about what kind of thing a poem is.