In 510 BC, Spartan troops helped the Athenians overthrow their king, the tyrant Hippias, son of Peisistratos. Cleomenes I, king of Sparta, put in place a pro-Spartan oligarchy headed by Isagoras. But his rival Cleisthenes, with the support of the middle class and aided by pro-democracy citizens, took over. Cleomenes intervened in 508 and 506 BC, but could not stop Cleisthenes, now supported by the Athenians. Through Cleisthenes’ reforms, the people endowed their city with isonomic institutions—equal rights for all citizens (though only men were citizens)—and established ostracism.
The isonomic and isegoric (equal freedom of speech) democracy was first organized into about 130 demes, which became the basic civic element. The 10,000 citizens exercised their power as members of the assembly (ἐκκλησία, ekklesia), headed by a council of 500 citizens chosen at random.
The city’s administrative geography was reworked, in order to create mixed political groups: not federated by local interests linked to the sea, to the city, or to farming, whose decisions (e.g. a declaration of war) would depend on their geographical position. The territory of the city was also divided into thirty trittyes as follows:
A tribe consisted of three trittyes, selected at random, one from each of the three groups. Each tribe therefore always acted in the interest of all three sectors.
It was this corpus of reforms that allowed the emergence of a wider democracy in the 460s and 450s BC.