-burg) 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. The metropolitan population of 2,353,045 is the largest in both the Ohio Valley and Appalachia, the second-largest in Pennsylvania (behind Philadelphia), and the 26th-largest in the U. 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.
A 1769 survey referenced the future city as the "Manor of Pittsburgh".
Both the Colony of Virginia and the Province of Pennsylvania claimed the region under their colonial charters until 1780, when they agreed under a federal initiative to extend the Mason–Dixon line westward, placing Pittsburgh in Pennsylvania.
The area has served as the long-time federal agency headquarters for cyber defense, software engineering, robotics, energy research and the nuclear navy. "Be it enacted by the Pennsylvania State Senate and Pennsylvania House of Representatives of the Commonwealth of Pennsylvania..the authority of the same, that the said town of Pittsburgh shall be...erected into a borough, which shall be called the borough of Pittsburgh for ever." European pioneers, primarily Dutch, followed in the early 18th century.Lord Jeffrey Amherst ordered blankets contaminated from smallpox victims to be distributed in 1763 to the tribes surrounding the fort.The disease spread into other areas, infected other tribes, and killed hundreds of thousands.By the 1840s, Pittsburgh was one of the largest cities west of the Allegheny Mountains.The Great Fire of Pittsburgh destroyed over a thousand buildings in 1845.The city features 30 skyscrapers, two inclined railways, a pre-revolutionary fortification and the Point State Park at the confluence of the rivers.