river in northern England, flowing for 62 miles (100 km) into the North Sea below Newcastle upon Tyne. It is formed near Hexham by the confluence of the North Tyne, with its tributary the Rede, and the South Tyne. From Wylam the Tyne is the boundary between the historic counties of Northumberland and Durham. The river crosses a coalfield and for its last 14 miles (23 km) is a tidal waterway. Since about 1850 the Tyne Improvement Commission has carried out dredging on the lower river, dock construction, and improvement of the entrance. The historic crossing is from Gateshead to Newcastle upon Tyne, 10 miles (16 km) from the mouth. The Tyne shipped coal for at least six centuries, and its estuary is now lined with industry and large urban communities constituting the Tyne and Wear metropolitan area, but for most of their courses the river and its tributaries flow through unspoiled countryside. Much of the Tyne basin, including the first section of the Roman Hadrian's Wall, lies within the Northumberland National Park.