Philadelphia, colloquially referred to as Philly, is the most populous city in the U.S. state of Pennsylvania and the sixth-most populous city in the United States, with a population of 1,603,797 in the 2020 census. The city is the urban core of the larger Delaware Valley, also known as the Philadelphia metropolitan area, the nation's eighth-largest metropolitan area and seventh-largest combined statistical area with 6.245 million residents and 7.366 million residents, respectively. Philadelphia has played an extensive role in United States history. The city was founded in 1682 by William Penn, an English Quaker and advocate of religious freedom, and served as the capital of the Pennsylvania Colony during the British colonial era. The city went on to play a historic and vital role during the American Revolution and Revolutionary War, serving as the central meeting place for the nation's founding fathers, hosting the First Continental Congress in 1774, preserving the Liberty Bell, and hosting the Second Continental Congress during which the nation's 56 founders formed the Continental Army and elected George Washington as its commander in 1775, and unanimously adopted the Declaration of Independence on July 4, 1776. For nine months, from September 1777 to June 1778, the city fell under British occupation during the war's Philadelphia campaign. In 1787, the U.S. Constitution was ratified in Philadelphia at the Philadelphia Convention. Philadelphia remained the nation's largest city until 1790, and it served as the nation's first capital from May 10, 1775, until December 12, 1776, and on four subsequent occasions until 1800, when construction of the new national capital in Washington, D.C. was completed. Philadelphia maintains extensive contemporary influence in business and industry, culture, sports, and music. With 17 four-year universities and colleges in the city, Philadelphia is one of the nation's leading centers for higher education and academic research. The city is a national cultural center, hosting more outdoor sculptures and murals than any other city in the nation. Fairmount Park, when combined with adjacent Wissahickon Valley Park in the same watershed, is 2,052 acres (830 ha), representing one of the nation's largest and the world's 54th-largest urban park. Philadelphia is known for its arts, culture, cuisine, and colonial and Revolutionary-era history; in 2016, it attracted 42 million domestic tourists who spent $6.8 billion, representing $11 billion in economic impact to the city and its surrounding Pennsylvania counties. With five professional sports teams and one of the nation's most loyal and passionate fan bases, Philadelphia is often ranked as the nation's best city for professional sports fans. The city has a culturally and philanthropically active LGBTQ+ community. Philadelphia also has played an immensely influential historic and ongoing role in the development and evolution of American music, especially R&B, soul, and rock. As of 2022, the Philadelphia metropolitan area had a gross metropolitan product of US$518.5 billion and is home to five Fortune 500 corporate headquarters. Metropolitan Philadelphia ranks as one of the Big Five U.S. venture capital hubs, facilitated by its geographic proximity to both the entrepreneurial and financial ecosystems of New York City and to the federal regulatory environment of Washington, D.C. Greater Philadelphia is also a biotechnology hub. The Philadelphia Stock Exchange, owned by Nasdaq since 2008, is the nation's oldest stock exchange and a global leader in options trading. 30th Street Station, the city's primary rail station, is the third-busiest Amtrak hub in the nation, and the city's multimodal transportation and logistics infrastructure also includes Philadelphia International Airport, a major transatlantic gateway and transcontinental hub; the rapidly-growing PhilaPort seaport; and Interstate 95, the spine of the north–south highway system along the U.S. East Coast. Philadelphia is a city of many firsts, including the nation's first library (1731), hospital (1751), medical school (1765), national capital (1774), university (by some accounts) (1779), central bank (1781), stock exchange (1790), zoo (1874), and business school (1881). Philadelphia contains 67 National Historic Landmarks, including Independence Hall. From the city's 17th century founding through the present, Philadelphia has been the birthplace or home to an extensive number of prominent and influential Americans.