In 1646 Pope Innocent X entrusted Borromini with the renovation of the basilica interior, but he set some limits to Borromini's ingenuity as he wanted the floor and the ceiling of the main nave to be preserved. The floor went back to the time of Pope Martin V (1417-31), whereas the ceiling was a work by Flaminio Boulanger and showed the coats of arms of Pope Pius IV and Pope Pius V.