http://agathe.gr/democracy/practice_of_ostracism.html
Ostracism Soon after their victory over the Persians at the battle of Marathon in 490 B.C., the Athenians began the practice of ostracism, a form of election designed to curb the power of any rising tyrant ... And when ignoble men of the baser sort came to be subjected to this penalty it ceased to be inflicted at all, and Hyperbolos was the last to be thus ostracized. It is said that Hyperbolos was ostracized for the following reason. ... Accordingly, when the people were about to exercise the ostracism, and were clearly going to vote against one or the other of these two men, they came to terms with one another, united their opposing factions, and effected the ostracism of Hyperbolos. The people were incensed at this for they felt that the institution had been insulted and abused, and so they abandoned it utterly and put an end to it.