After the great Peloponessian wars Sparta installed oligarchies in the cities of several former allies of Athens. Often these oligarchies consisted of ten men, the so-called decarchies, which were supported by a Spartan garrison lead by a reconciler, who's main function it was to collect taxes for Sparta. One of the cities that got an oligarchy was Athens: Sparta installed an oligarchy of thirty men here in 404.
Under the personal pressure of Lysander, the Spartan admiral who had a keyrole during the Peloponessian wars, recognised the people's council of Athens this committee of thirty, and gave it all the power to these men. The assignment of the committee was formally to create a structure in the laws of Athens, which had become messy due to their increasing number during the fifth century. The real reason was of course to prevent Athens from becoming a democracy again, and thus a threat to Sparta. That is why it is not surprising that all thirty members were very much against democracy, who were lead by the extremist Critias. Without any shame did he bring the sophistic theory of the right of the strongest into practise: democratic benefits disappeared, and many democrats and rich citizens became the victim of a number of mock trials that were covered up by Lysander.
Guerilla against the committee.
The Spartan king Pausanias, a grandson of the Pausanias who had won the battle of Plataea during the Persian wars, and most conservatives were not too happy with the strong position of Lysander. Lysander was no Spartan king, but his political ambitions were a serious threat thanks to his good relationship with the Persian king Cyrus II, and his victories on the battlefield. Athenian democrats had already started a guerrilla war from Thebes against the committee. They had managed to conquer the Piraeus, and Critias was killed during this action. The outcome of the subsequent civil war between Piraeus and Athens was decided by Pausanias who chose the side of the democrats in order to reduce the strength of Lysander. The democrats granted a political amnesty, and they did finish the revision of the laws.
The council of 500 assigned 500 nomothetes, or interpreters of the laws. The suggestions of these 500 nomothetes were not approved by the people's council, but by another group of 500 nomothetes who were chosen by the people. Another change was that an already existing law could no any longer be ignored. Each year the people's council was asked if the current set of laws had to be changed. If this needed to happen then ad hoc committee was formed from the 500 nomothetes who were chosen by the people.
This revision of the laws, and the change in the judicial structure, implied that normal suggestion to the people's council had to agree with the existing laws. Was this not the case then the person who suggested it could be sued, such a trial was called a graphe paranomoon. A politician who was found guilty three times during such a trial lost his citizenship, while a prosecutor lost it after the first time. The reason for this voluntary curtailment of the people's council was that it slowed down the influence of demagogues.