The London Borough of Tower Hamlets forms the core of the East End. It lies east of the ancient walled City of London and north of the River Thames. Use of the term "East End" in a pejorative sense began in the late 19th century, as the expansion of the population of London led to extreme overcrowding throughout the area and a concentration of poor people and immigrants in the districts that made it up. These problems were exacerbated with the construction of St Katharine Docks (1827) and the central London railway termini (1840–1875) that caused the clearance of former slums and rookeries, with many of the displaced people moving into the area. Over the course of a century, the East End became synonymous with poverty, overcrowding, disease and criminality.