Peterborough is a Cathedral City and Unitary Authority Area in the East of England, with a population estimated in 2012 to be 186,400, of which 137,910 were residents in the urban area of the city. For ceremonial purposes it falls within the county of Cambridgeshire. It is the largest city in Cambridgeshire and the 27th largest in the United Kingdom, excluding urban zones. Situated 75 miles (121 km) north of London, the city stands on the River Nene which flows into the North Sea approximately 30 miles (48 km) to the north-east. The railway station is an important stop on the East Coast Main Line between London and Edinburgh. The unitary authority borders Northamptonshire and Rutland to the west, Lincolnshire to the north, and Cambridgeshire to the south and east.The local topography is flat and low-lying, and in some places lies below sea level, for example in the Fens that lie to the east of Peterborough. Human settlement in the area began before the Bronze Age, as can be seen at the Flag Fen archaeological site to the east of the current city centre also with evidence of Roman occupation. The Anglo-Saxon period saw the establishment of a monastery, Medeshamstede, which later became Peterborough Cathedral. Peterborough was until 1965 part of Northamptonshire, although the city with its surrounding rural area was from medieval times administered separately as the Soke of Peterborough.