Frankfurt am Main, English Frankfurt on the Main, Römer [Credit: The J. Allan Cash Photolibrary, London]city, Hessen Land (state), western Germany. The city lies along the Main River about 19 miles (30 km) upstream from its confluence with the Rhine River at Mainz. Pop. (2011) city, 667,925; (2000 est.) urban agglom., 3,681,000Frankfurt am Main was a free imperial city from 1372 until 1806, when Napoleon I made it the seat of government for the prince primate of the Confederation of the Rhine. In 1810 the city became the capital of the Grand Duchy of Frankfurt, created by Napoleon. From 1815, when Napoleon fell, Frankfurt was again a free city, where in 1848–49 the Frankfurt National Assembly met. From 1816 to 1866 the city was the seat of the German Bundestag (Federal Diet) and thus the capital of Germany. After the Seven Weeks’ War in 1866, Frankfurt was annexed by Prussia and thereby lost its free-city status. It was only after its integration into a united Germany that Frankfurt developed into a large industrial city.