The city of Philadelphia is the largest city in Pennsylvania and the sixth most populous city in the United States. It is the county seat of Philadelphia County. It is colloquially referred to as "the City of Brotherly Love" (from Greek: Φιλαδέλφεια, /fi.la.ˈdɛl.fɛj.a/, "brotherly love" from philos "love" and adelphos "brother").
In 2005 the United States Census Bureau estimated the population of the city proper to be 1.4 million. Philadelphia is a major commercial, educational, and cultural center for the nation. As of the 2006 population estimate, the Philadelphia metropolitan area was the fifth-largest in the United States with a population of 5.8 million.
In the 18th century, the city was the first capital and most populous city of the United States. It was the second largest city, behind London, in the British Empire. Also, at that time, it eclipsed Boston and New York City in political and social importance, with Benjamin Franklin taking a large role in Philadelphia's rise. It was the social and geographical center of the original 13 American colonies. It was in this city that thoughts, and subsequent actions, gave birth to the American Revolution and to the American ideals of liberty, democracy and independence.