The institution of ostracism, believed to have been created by Cleisthenes, was not actually used until 487 BC; some 20 years after his reforms.

Designed as a safeguard for protecting democracy, it was a harsh and unforgiving punishment, often meted out to individuals who were becoming too personally powerful, or who threatened the positions of those who already had great influence.

Ostracism literally means 'judgement by shards' because shards of pottery, the cheapest writing material, were used for the voting. Once a year, the popular assembly would take a vote to decide whether ostracism was to be held that year. If so, two months later the question would be put to the people in a strictly supervised meeting within the agora, or marketplace. Citizens would scratch on to their pottery shard - or have scratched for them - the name of the person they wanted ostracized. The top name on the list would then be exiled from Athens for 10 years.

A quorum, or minimum number, of 6000 citizens was required for the vote to be valid.