Pittsburgh is a city in the Commonwealth of Pennsylvania in the United States, and is the county seat of Allegheny County. As of 2017, a total population of 305,704 lives within the city limits, making it the 63rd-largest city in the U.S. The metropolitan population of 2,353,045 is the largest in both the Ohio Valley and Appalachia, the second-largest in Pennsylvania, and the 26th-largest in the U.S.Located at the confluence of the Allegheny, Monongahela, and Ohio rivers, Pittsburgh is known as both "the Steel City" for its more than 300 steel-related businesses, and as the "City of Bridges" for its 446 bridges. The city features 30 skyscrapers, two inclined railways, a pre-revolutionary fortification and the Point State Park at the confluence of the rivers. The city developed as a vital link of the Atlantic coast and Midwest, as the mineral-rich Allegheny Mountains made the area coveted by the French and British empires, Virginians, Whiskey Rebels, and Civil War raiders.