Under the Roman Empire (when it was known as Danubius and, in its lower course, as Ister), the Danube was the northern border against the barbarian world. As Rome declined, the Danubian plains for centuries attracted invading hordes—Goths, Huns, Avars, Magyars, Pechenegs, Cumans, Mongols, and others. The Danube increased in commercial importance in the era of the Crusades, but commerce suffered (15th–16th cent.) after the Turks gained control of its course from the Hungarian plain to the Black Sea. In the 19th cent. the Danube's economic importance as an international waterway increased. At the end of the Crimean War the Congress of Paris appointed (1856) a commission to clear the delta (below Brăila) of obstructions.
By the Treaty of Versailles (1919) the Danube was internationalized and a commission established with jurisdiction over the course from Ulm to Brăila. Germany repudiated the internationalization in 1936 and in 1939–40 forced both the navigation and international commissions to dissolve. After World War II, delegates from Czechoslovakia, Hungary, Yugoslavia, Romania, Bulgaria, the Soviet Union, the United States, Great Britain, and France met (1948) to determine the status of the Danube. When a commission representing only the seven riparian nations was established, the three Western nations refused to sign the convention. Subsequently, the riparian nations established a new Danube commission, based at Budapest; present membership includes Austria, Bulgaria, Croatia, Germany, Hungary, Moldova, Romania, Russia, Serbia, Slovakia, and Ukraine.