Athens was the birthplace of democracy, however for most of its history the democracy was more in theory than in practice with either tyrants or oligarchical elements in control.  In part, this was because Athens was just too large for a pure democracy to be practical.  Plato had felt that the ideal number for a polis was about 5,000 citizens, but Athens had over 21,000 citizens eligible to participate in the Assembly, which met forty times a year.