After their victory in the Peloponnesian War the Spartans imposed on Athens an oligarchic regime made up of thirty members. The government of the Thirty effected massive executions of the democrats.
Bouchard, Elsa. "Establishment of the Thirty Tyrants at Athens". The Literary Encyclopedia. First published 01 March 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=11244, accessed 12 March 2014.]