 The oligarchs, led by Critias, one of the "overseers" and a former exile, summoned a Spartan garrison to ensure their safety and then initiated a reign of terror, executing any men who they thought might possess sufficient initiative or a large enough following to effectively challenge them.It was this campaign that first drove a wedge between Theramenes and the leaders of the Thirty; initially a supporter of Critias, Theramenes now argued that it was unnecessary to execute men who had shown no sign of wishing the oligarchy harm just because they had been popular under the democracy.This protest, however, failed to slow the pace of the executions, so Theramenes next argued that, if the oligarchy was to govern by force, it must at least expand its base; fearful that Theramenes might lead a popular movement against them, Critias and the leaders of the Thirty issued a list of 3,000 men who would be associates in the new government.