Eurojust was established as a result of a decision that the European Council of Tampere (15–16 October 1999) made to set up a permanent judicial co-operation unit in order to improve the fight against serious crime. The Treaty of Nice amended the Treaty on the European Union to include a reference to Eurojust. On 14 December 2000, a precursor organization called Pro-Eurojust was created by the Council of the European Union to permit prosecutors to test the Eurojust processes. It began operating in Brussels on 1 March 2001. The terrorist attacks in the U.S. in September of that year demonstrated strongly the need for international cooperation, speeding the development of Eurojust, which was then established in February 2002 by Council Decision 2002/187/JHA. The new organization settled in The Hague on 29 April 2003.