The Thirty Tyrants (οἱ τριάκοντα τύραννοι, hoi triákonta týrannoi) were a pro-Spartan oligarchy installed in Athens in 404 BC, after the Athenian democracy had been defeated by Sparta in the Peloponnesian War. Upon Lysander's request, the Thirty were elected as a tyrannical government, not just as a legislative committee. Although they maintained power for only a brief eight months, their reign resulted in the killing of 5% of the Athenian population, the confiscation of citizens' property and the exile of other democratic supporters. They became known as the "Thirty Tyrants" because of their cruel and oppressive tactics. The two leading members were Critias and Theramenes.
With Spartan support, the Thirty established an interim government in Athens. The Thirty were concerned with the revision, if not erasure, of democratic laws inscribed on the wall next to the Stoa Basileios. Consequently, the Thirty reduced the rights of Athenian citizens in order to institute an oligarchical regime. The Thirty appointed a council of 500 to serve the judicial functions formerly belonging to all the citizens. However, not all Athenian men had their rights removed. In fact, the Thirty chose 3,000 Athenian men "to share in the government". These hand-selected individuals had the right to carry weapons, to have a jury trial, and to reside within city limits. The list of the selected 3,000 was constantly revised. Although little is known about these 3,000 men ‒ for a complete record was never documented ‒ it is hypothesised that the Thirty appointed these select few as the only men the Thirty could find who were devotedly loyal to their regime.
Led by Critias, the Thirty Tyrants presided over a reign of terror in which they executed, murdered, and exiled hundreds of Athenians, seizing their possessions afterward. Both Isocrates and Aristotle (the latter in the Athenian Constitution) have reported that the Thirty executed 1,500 people without trial.