The floor of the church is of the ancient mosaic known as Opus Alexandrinum. The nave is separated from the aisles by twenty-two ancient columns, of which two are of cipollino, two of white marble, and eighteen of Egyptian granite. They are of very different forms and sizes, and have probably been collected from various pagan edifices. The inscription "A Cubiculo Augustorum" upon the third column on the left of the nave, shows that it was brought from the Palace of the Cæsars. The windows in this church are amongst the few in Rome which show traces of gothic. At the end of the nave, on either side, are two ambones, marking the position of the choir before it was extended to its present site in the sixteenth century. The transepts are full of interesting monuments. That on the right is the burial-place of the great family of Savelli, and contains--on the left, the monument of Luca Savelli, 1266 (father of Pope Honorius IV.) and his son Pandolfo,--an ancient and richly sculptured sarcophagus, to which a gothic canopy was added by _Agostino_ and _Agnolo da Siena_ from designs of Giotto. Opposite, is the tomb of the mother of Honorius, Vana Aldobrandesca, upon which is the statue of the pope himself, removed from his monument in the old St. Peter's by Paul III. On the left of the high altar is the tomb of Cardinal Gianbattista Savelli, ob. 1498, and near it--in the pavement, the half-effaced gravestone of Sigismondo Conti, whose features are so familiar to us from his portrait introduced into the famous picture of the Madonna di Foligno, which was painted by Raphael at his order, and presented by him to this church, where it remained over the high altar, till 1565, when his great niece Anna became a nun at the convent of the Contesse at Foligno, and was allowed to carry it away with her. In the east transept is another fine gothic tomb, that of Cardinal Matteo di Acquasparta (1302), a General of the Franciscans mentioned by Dante for his wise and moderate rule.[46] The quaint chapel in the middle of this transept, now dedicated to St. Helena, is supposed to occupy the site of the "Ara Primogeniti Dei." Upon the pier near the ambone of the gospel is the monument of Queen Catherine of Bosnia, who died at Rome in 1478, bequeathing her states to the Roman Church on condition of their reversion to her son, who had embraced Mahommedanism, if he should return to the Catholic faith. Near this, upon the transept wall, is the tomb of Felice de Fredis, ob. 1529, upon which it is recorded that he was the finder of the Laocoon. The Chapel of the Annunciation, opening from the west isle, has a tomb to G. Crivelli, by Donatello, bearing his signature, "Opus Donatelli Florentini." The Chapel of Santa Croce is the burial-place of the Ponziani family, and was the scene of the celebrated ecstasy of the favourite Roman saint Francesca Romana.