Comcast Center, also known as the Comcast Tower, is a skyscraper in Center City, Philadelphia, Pennsylvania, United States. The 58-story, tower is the second-tallest building in Philadelphia and the state of Pennsylvania, as well as the twenty-third tallest building in the United States. Originally called One Pennsylvania Plaza when the building was first announced in 2001, the Comcast Center went through two redesigns before construction began in 2005. Comcast Center was designed by Robert A.M. Stern Architects for Liberty Property Trust.