Pittsburgh (pron.: /ˈpɪtsbərɡ/, PITS-burg) is the seat of Allegheny County and with a population of 307,484 is the second-largest city in the U.S.Commonwealth of Pennsylvania. With a metropolitan CSA population of 2,661,369 it is the largest in both the Ohio Valley and Appalachia and the 22nd-largest in the U.S. Pittsburgh is known as both "the Steel City" for its more than 300 related businesses and "the City of Bridges" for its world record 446 bridges. The city also features 27 skyscrapers, two inclined railways, a pre-revolutionary fortification, and the source of the Ohio at the confluence of the Monongahela and Allegheny. This vital link of the Atlantic coast and the Mid-west cuts through the mineral-rich Alleghenies and made the Pittsburgh area coveted by the French and British empires, Virginia, Whiskey Rebels, Civil War raiders and media networks.