Paris, Congress of, 1856, conference held by representatives of France, Great Britain, the Ottoman Empire (Turkey), Sardinia, Russia, Austria, and Prussia to negotiate the peace after the Crimean War. In the Treaty of Paris (Mar. 30, 1856), Russia agreed to the neutralization of the Black Sea, which was to be closed to war vessels and opened to the merchant marines of all nations. The Danubian principalities (Moldavia and Walachia, after 1859 called Romania) were recognized as quasi-independent states under Ottoman suzerainty; to them Russia ceded the left bank of the mouth of the Danube and part of Bessarabia. The lower Danube was placed under an international commission. The boundaries of Russia and the Ottoman Empire in Asia were restored to their prewar limits (to the detriment of Russia). The Ottoman Empire became a member of the European concert, and its integrity was guaranteed; the sultan in turn promised to improve the status of his Christian subjects. Several principles of international law were adopted by the congress in the Declaration of Paris. The provisions of the treaty were altered (1878) by the Congress of Berlin.