From the sacristy a staircase leads to the _Lower Church_ (occasionally illuminated for the public) first discovered in 1857. Here, there are several pillars of the rarest marbles in perfect preservation, and a very curious series of frescoes of the eighth and ninth centuries, parts of which are still clear and almost uninjured. These include--the Crucifixion, with the Virgin and St. John standing by the cross,--the earliest example in Rome of this well-known subject; the Ascension, sometimes called by Romanists (in preparation for their dogma of 1870), "the Assumption of the Virgin," because the figure of the Virgin is elevated above the other apostles, though she is evidently intent on watching the retreating figure of her divine Son--in this fresco the figure of a pope is introduced (with the square nimbus, showing that it was painted in his lifetime), and the inscription "Sanctissimus dominus, Leo Papa Romanus," probably Leo III. or Leo IV.; the Maries at the sepulchre; the descent into Hades; the Marriage of Cana; the Funeral of St. Cyril with Pope Nicholas I. (858--67) walking in the procession; and, the most interesting of all--probably of somewhat later date, the story of S. Clemente, and that of S. Alexis, whose adventures are described in the account of his church on the Aventine. An altar of Mithras was discovered during the excavations here. Beneath this crypt is still a third structure, discovered 1867,--probably the very house of St. Clement,--(decorated with rich stucco ornament)--sometimes supposed to be the 'cavern near S. Clemente' to which the Emperor Otho III., who died at the age of twenty-two, retired in A.D. 999 with his confessor, and where he spent fourteen days in penitential retirement. According to the Acts of the Martyrs, the Prefect Mamertinus ordered the arrest of Pope Clement, and intended to put him to death, but was deterred by a tumult of the people, who cried with one voice, "What evil has he done, or rather what good has he not done?" Clement was then condemned to exile in the Chersonese, and Mamertinus, touched by his submission and courage, dismissed him with the words--"May the God you worship bring you relief in the place of your banishment."