 The sea of iron pillars holding up the PRR's elevated trackbed was replaced in the 1890s by a 10-block stone viaduct to the Schuylkill River.This created a block-wide barrier known as "The Chinese Wall", cutting the western portion of the city in half and discouraging development there.At the time, most commercial activity in Center City was east of Broad Street, which is why the SEPTA Market-Frankford Line has no stops between 30th Street Station and 15th Street.