Cleomenes I (klēŏmˈĭnēz) [key], d. c.489 B.C., king of Sparta after 518 B.C. In accordance with Sparta's policy of helping oligarchies in other states at the expense of the tyrants or the people, Cleomenes joined the Athenians in ousting the tyrant Hippias, but to Cleomenes' dismay Cleisthenes, the principal Athenian aristocrat, sided with the people and took the power (510 B.C.). Twice Cleomenes attacked democratic Athens. The first time he expelled Cleisthenes, who, however, quickly returned to power, thus halting Spartan influence. The second time Corinth checkmated Sparta by refusing to help in an attack that would have disturbed the balance of power. Cleomenes' reputation for ruthlessness is due chiefly to his attack (c.494 B.C.) on Argos, in which he slaughtered 6,000 Argives—an exploit that gave Sparta hegemony in S Greece for many years.
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