The Cathedral Basilica of Saints Peter and Paul, head church of the Roman Catholic Archdiocese of Philadelphia, is located at 18th Street and the Benjamin Franklin Parkway, on the east side of Logan Square in Philadelphia. It was built between 1846 and 1864, and was designed by Napoleon LeBrun, from original plans by the Reverend Mariano Muller and the Reverend John B. Tornatore, with the dome and Palladian facade, designed by John Notman, added after 1850. The interior was largely decorated by Constantino Brumidi.

John Notman was a Scottish-born American architect and landscape architect based in Philadelphia. He designed buildings, cemeteries, churches and country estates in the Mid-Atlantic region of the United States and helped popularize Italianate architecture in the United States.