Aix-la-Chapelle, Congress of (1818), a meeting of the members of the Quadruple Alliance—Great Britain, Austria, Prussia, and Russia. The congress agreed to remove the occupation armies that had been kept in France since the defeat of Napoleon in 1815. France was then admitted to the group, creating the informal Quintuple Alliance. Alexander I of Russia, sponsor of the Holy Alliance, tried unsuccessfully to turn this alliance into a police force to put down all democratic and liberal movements in Europe. The five countries did form the so-called Concert of Europe; they agreed to meet at intervals to preserve peace and to consider common problems.