Philadelphia is the largest city in the Commonwealth of Pennsylvania, the fifth-most-populous city in the United States, and the core of the sixth-largest metropolitan area in the country. Located in the Northeastern United States at the confluence of the Delaware and Schuylkill rivers, Philadelphia is the economic and cultural center of the. The population of the city — Pennsylvania's only consolidated city-county — was measured at 1,526,006 in and estimated at 1,553,165 in 2013, according to the United States Census Bureau. The five Pennsylvania counties nearest Philadelphia have a total population of 4,008,994, while its Metropolitan Statistical Area, which includes parts of four states, is home to more than 6 million people. Popular nicknames for Philadelphia are Philly and The City of Brotherly Love, the latter of which comes from the literal meaning of the city's name in Greek ("brotherly love", compounded from philos (φίλος) "loving", and adelphos (ἀδελφός) "brother").In 1682, William Penn founded the city to serve as capital of Pennsylvania Colony. By the 1750s, Philadelphia had surpassed Boston to become the largest city and busiest port in British America, and second in the British Empire, behind London. During the American Revolution, Philadelphia played an instrumental role as a meeting place for the Founding Fathers of the United States, who signed the Declaration of Independence in 1776 and the Constitution in 1787. Philadelphia was one of the nation's capitals during the Revolutionary War, and the city served as the temporary U.S. capital while Washington, D.C., was under construction. During the 19th century, Philadelphia became a major industrial center and railroad hub that grew from an influx of European immigrants. It became a prime destination for African Americans during the Great Migration and surpassed two million occupants by 1950.