In railroading's golden age, the B&O was one of several trunk lines uniting the northeast quadrant of the United States into a wide industrial zone. It was the southern border as the New York Central was the northern border. The Pennsylvania Railroad controlled the center, and smaller roads like the Lackawanna, Lehigh Valley, and the Erie in the center surviving largely through the Interstate Commerce Commission. The corners of this map are Baltimore in the southeast, Boston in the northeast, Chicago in the northwest, and St. Louis in the southwest.