The Thirty Tyrants were a pro-Spartan oligarchy installed in Athens after Athens' defeat in the Peloponnesian War in April 404 BC. Its two leading members were Tharamenes and Critias, a former acolyte of Socrates.
The Thirty severely reduced the number of rights of Athenian citizens. Instead of all Athenians participating in legal functions, only a specially selected 500 could. Only 3,000 people had the right to carry weapons or receive a jury trial. Hundreds of Athenians were killed (they were ordered to drink hemlock) and thousands more were exiled.