Commissioned by King Ferdinand and Queen Isabella of Spain, on the site of 9th century chapel and supposed burial site of St. Peter. Titular Church served by the Franciscans. Many famous artists have contributed to the decoration of the church over the years, including: Francesco Fontana, Sebastiano del Piombo (nave frescos), Bramante (the Tempietto), Giovanni del Vecchio, Giorgio Vasari (altarpiece), and Bernini (Raimondi chapel).