Cleisthenes (//; Greek: Κλεισθένης, also Clisthenes or Kleisthenes) was a noble Athenian of the Alcmaeonid family. He is credited with reforming the constitution of ancient Athens and setting it on a democratic footing in 508/7 BC. For these accomplishments, historians refer to him as "the father of Athenian democracy." He was the maternal grandson of the tyrant Cleisthenes of Sicyon, as the younger son of the latter's daughter Agariste and her husband Megacles. Also, he was credited with increasing the power of the Athenian citizens’ assembly and for reducing the power of the nobility over Athenian politics. 
Rise to power
With help from the Alcmaeonidae (Cleisthenes' genos, "clan"), he was responsible for overthrowing Hippias, the tyrant son of Pisistratus. After the collapse of Hippias' tyranny, Isagoras and Cleisthenes were rivals for power, but Isagoras won the upper hand by appealing to the Spartan king Cleomenes I to help him expel Cleisthenes. He did so on the pretext of the Alcmaeonid curse. Consequently, Cleisthenes left Athens as an exile, and Isagoras was unrivalled in power within the city. Isagoras set about dispossessing hundreds of Athenians of their homes and exiling them on the pretext that they too were cursed. He also attempted to dissolve the Boule (βουλή), a council of Athenian citizens appointed to run the daily affairs of the city. However, the council resisted, and the Athenian people declared their support of the council. Isagoras and his supporters were forced to flee to the Acropolis, remaining besieged there for two days. On the third day they fled the city and were banished. Cleisthenes was subsequently recalled, along with hundreds of exiles, and he assumed leadership of Athens.
Contribution to the governance of Athens
After this victory Cleisthenes began to reform the government of Athens. In order to forestall strife between the traditional clans, which had led to the tyranny in the first place, he changed the political organization from the four traditional tribes, which were based on family relations, into ten tribes according to their area of residence (their deme). It is thought that there may have been 139 demes (though this is still a matter of debate) which were organized into three groups called trittyes ("thirds"), with ten demes divided among three regions in each trittyes (a city region, asty; a coastal region, paralia; and an inland region, mesogeia). Cleisthenes also abolished patronymics in favour of demonymics (a name given according to the deme to which one belongs), thus increasing Athenians' sense of belonging to a deme. He also established sortition - the random selection of citizens to fill government positions rather than kinship or heredity, a true test of real democracy. He reorganized the Boule, created with 400 members under Solon, so that it had 500 members, 50 from each tribe. He also introduced the bouletic oath, "To advise according to the laws what was best for the people". The court system (Dikasteria — law courts) was reorganized and had from 201–5001 jurors selected each day, up to 500 from each tribe. It was the role of the Boule to propose laws to the assembly of voters, who convened in Athens around forty times a year for this purpose. The bills proposed could be rejected, passed or returned for amendments by the assembly.
Cleisthenes also may have introduced ostracism (first used in 487 BC), whereby a vote from more than 6,000 of the citizens would exile a citizen for 10 years. The initial trend was to vote for a citizen deemed a threat to the democracy (e.g., by having ambitions to set himself up as tyrant). However, soon after, any citizen judged to have too much power in the city tended to be targeted for exile (e.g., Xanthippus in 485/84 BC). Under this system, the exiled man's property was maintained, but he was not physically in the city where he could possibly create a new tyranny.
Cleisthenes called these reforms isonomia ("equality vis à vis law", iso=equality; nomos=law), instead of demokratia. Cleisthenes’ life after his reforms is unknown as no ancient texts mention him thereafter.
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