The Pennsylvania Railroad (PRR), established in 1846 and headquartered in Philadelphia, was once the largest railroad and transportation company in the world. It was often called the “Standard Railroad of the World” due to its technological innovations, vast network, and financial dominance. The PRR originally built a rail line connecting Harrisburg and Pittsburgh, which opened for service in 1848, and later expanded to major cities including Chicago, New York City, St. Louis, and Washington, D.C. At its peak, the railroad operated over 11,600 miles of track and was the largest corporation globally by revenue and traffic.