Ostracism, a form of banishment introduced into Athens by Cleisthenes (q.v.). Its object was I to prevent any citizen who was conspicuous through his ability, riches, or popularity from acquiring too great power in the state. When the people had decided that an ostracism was necessary, a public meeting (ecclesia) was held in the market-place (agora), and the citizens voted by tribes, each depositing in a fixed spot an oyster-shell (ostrakon) on which was written the name of the person whose banishment he desired. The citizen who obtained the largest- number of these unfavourable votes was forced to leave Athens for ten years. A similar institution, "petalism," existed in Syracuse.