508 BC — Cleisthenes reorganizes Athens. He creates the deme, a local unit to serve as the basis of his political system. Citizenship is tightly linked to the deme, for each deme keeps the roll of those within its jurisdiction, who are admitted to citizenship. He groups all the demes into 10 tribes, which thus form the link between the demes and the central government. The central government includes an assembly of all citizens and a new council of 500 members.