Pittsburgh is the seat of
Allegheny County and with a population of 306,211 is the second-largest city in
the U.S. state of Pennsylvania. With a metropolitan CSA population of
2,661,369, it is the largest in both the Ohio Valley and Appalachia and the
20th-largest in the U.S. Pittsburgh is known as both "the Steel City"
for its more than 300 steel-related businesses and "the City of
Bridges" for its world-record 446 bridges. The city features 30
skyscrapers, 2 inclined railways, a pre-revolutionary fortification, and the
source of the Ohio at the confluence of the
