The northern border with Romania is 609 km. Most of the frontier (470 km) is formed by the river Danube from the mouth of the river Timok in the west to the city of Silistra in the east. The land border from Silistra to Cape Sivriburun at the Black Sea is 139 km long. The Danube, with steep bluffs on the Bulgarian side and a wide area of swamps and marshes on the Romanian side, is crossed by two bridges – New Europe Bridge between Vidin and Calafat, and Danube Bridge between Ruse and Giurgiu. There are 48 Bulgarian and 32 Romanian islands along the river Danube; the largest one, Belene (41 km2), belongs to Bulgaria. The land frontier has three border crossings at Silistra, Kardam and Durankulak at the Black Sea. It is also crossed by a major gas pipeline transporting natural gas from Russia to Bulgaria.