Each polis had merely one king , with the sole exception of Sparta that had two . Kingship could be hereditary or by election for a limited period of time then , the king was to be elected again by people . The king also could be elected once for his life time , having the duties of leading the army during war , running the polis' affaires , summoning citizens for voting on important issues and leading them during the official worship . In some polises , the noblemen expelled the king and took over his office , and therefore were called tyrants .
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