Newcastle upon Tyne commonly known as Newcastle, is a city in the metropolitan county of Tyne and Wear in the North East of England. It is situated on the north western bank of the River Tyne's estuary and centred 8.5 mi (13.7 km) from the North Sea. The city is the most populous city in North East region and lies at the urban core of the Tyneside, the seventh most populous conurbation in the United Kingdom and the most populous in the North East. Newcastle is a member of the English Core Cities Group and with Gateshead the Eurocities network of European cities. Newcastle was part of the county of Northumberland until 1400 when it became a county of itself; a status it retained until becoming part of the Tyne and Wear metropolitan county in 1974.