Athenian politician, of the Alcmaeonid family, son of Megacles and Agaristē, daughter of Cleisthenes (1) of Sicyon. He was archon (see archontes) under the tyrant Hippias (1) in 525/4 bc, but later in Hippias' reign the Alcmaeonids went into exile and put pressure on Sparta through the Delphic oracle to intervene in Athens and overthrow the tyranny. In the power vacuum which followed, Cleisthenes and Isagoras were rivals for supremacy; Isagoras obtained the archonship for 508/7; but Cleisthenes appealed for popular support with a programme of reform. Isagoras appealed to King Cleomenes I of Sparta, who came to Athens with a small force, invoked the hereditary curse of the Alcmaeonids, and forced Cleisthenes and others to withdraw; but he met with strong popular resistance and was forced to withdraw in turn, taking Isagoras with him. Cleisthenes returned, and his reforms were enacted and put into effect.
Cleisthenes' main achievement was a new organization of the citizen body. The four Ionian tribes (phylai) and other older units were deprived of political significance. For the future each citizen was to be a member of one of 139 local units called demes (dēmoi, see demos), and the demes were grouped to form 30 new trittyes (‘thirds’) and 10 new phylai; citizenship and the political and military organization of Attica were to be based on these units (e.g. Solon's council, boule, of 400 became a council of 500, with 50 members from each tribe and individual demes acting as constituencies). The main purpose of the reform was probably to undermine the old channels of influence (and perhaps to give the Alcmaeonids an advantageous position in the new system); its main appeal to the ordinary citizens was perhaps the provision of political machinery at local level; and working this machinery educated the citizens towards democracy. (See democracy, athenian.) The institution of ostracism is almost certainly to be attributed to Cleisthenes.
In the 5th cent. Cleisthenes came to be regarded as the founder of the democracy, but in the political disputes at the end of the century the democrats looked further back, to Solon or even to Theseus.
Subjects: Classical studies