The Ancient Greeks believed there were two models of rule, democracy and tyranny. These were perpetually locked in a cycle of alternating power exchanges. Like the passage of the tides, there was a rhythmic, even predictable flow to their ascendancy: one system would rise, swell, peak, and then, eventually, ebb and recede. After a time, the old system would return. Sometimes these periods of rule were very long, and sometimes they were very short, but the cycle itself was considered eternal.