Pittsburgh (pronounce /ˈpɪtsbɚg/ (originally pronounced /ˈpɪtsb(ə)rə/)) is the second largest city in the Commonwealth of Pennsylvania with a population of 334,563 and the 20th largest metropolitan area in the United States, and the 50th largest metropolitan area in North America, with a population of 2,358,695. It is the county seat of Allegheny County, Pennsylvania. Built on land surrounding the confluence of the Allegheny and Monongahela rivers, where they merge to form the Ohio river, Pittsburgh features a skyline of 151 high-rise buildings, 446 bridges, two inclined railways and a pre-revolutionary fortification. Residents of the city are called Pittsburghers. The downtown area is located on the triangular parcel at the confluence of the rivers. Pittsburgh is noted for bridges of all types throughout the city and is commonly known as the "The City of Bridges" or "The Bridge Capital" of the United States. Pittsburgh's other nickname is "The Steel City" due to its one-time prominence in steel making.