The Athenian Coup of 411 BC was a revolutionary movement during the Peloponnesian War between Athens and Sparta that overthrew the democratic government of ancient Athens and replaced it with a short-lived oligarchy known as The Four Hundred. The movement was led by a number of prominent and wealthy Athenians who held positions of power in the Athenian army at Samos, in coordination with Alcibiades (and Antiphon) who promised to deliver Persian support to Athens if the democracy was overthrown. Negotiations with Alcibiades eventually broke down as he proved incapable of delivering his promise. Nevertheless, the leaders of the oligarchic movement went forward with their plans to overthrow Athenian democratic government.
The Four Hundred government in Athens suffered from instability as conflict soon arose between moderates and extremists among the oligarchs. The moderates, led by Theramenes and Aristocrates, called for the replacement of The Four Hundred with a broader oligarchy of “the 5,000” […]. After the leader of the extremists Phrynichus was assassinated, the moderates grew bolder and arrested an extremist general in Piraeus. A confrontation ensued, which ended with the hoplites in Piraeus tearing down the new fortification. Several days later, the Four Hundred were officially replaced by “the 5,000”, who ruled for several more months until after the Athenian victory at Cyzicus.
The Oligarchic Coup in Athens (Brewminate Blog)
Council of the Four Hundred (Britannica)
The Oligarchic Coup of 411 (Thomas R. Martin/Tufts University)
Athenian Coup of 411 (Wikipedia)