On entering the nave the visitor was struck by the simplicity of Constantine's design, and by the multitude and variety of later additions, by which the number of altars alone had been increased from one to sixty-eight. Ninety-two columns supported an open roof, the trusses of which were of the kingpost pattern. In spite of frequent repairs, resulting from fires, decay, and age, some of these trusses still bore the mark of Constantine's name. They were splendid specimens of timber. Filippo Bonanni, whose description of S. Peter's deserves more credit than all the rest together, except Grimaldi's manuscripts,[82] says that on February 21, 1606, he examined and measured the horizontal beam of the first truss from the façade, which Carlo Maderno had just lowered to the floor; it was seventy-seven feet long and three feet thick. The same writer copies from a manuscript diary of Rutilio Alberini, dated 1339, the following story relating to the same roof: "Pope Benedict XII. (1334-1342) has spent eighty thousand gold florins in repairing the roof of S. Peter's, his head carpenter being maestro Ballo da Colonna. A brave man he was, capable of lowering and lifting those tremendous beams as if they were motes, and standing on them while in motion. I have seen one marked with the name of the builder of the church (CON_stantine_); it was so huge that all kinds of animals had bored their holes and nests in it. The holes looked like small caverns, many yards long, and gave shelter to thousands of rats." Grimaldi climbed the roof at the beginning of 1606, and describes it as made of three kinds of tiles,--bronze, brick, and lead. The tiles of gilt bronze were cast in the time of the emperor Hadrian for the roof of the Temple of Venus and Rome. Pope Honorius I. (625-640) was allowed by Heraclius to make use of them for S. Peter's. The brick tiles were all stamped with the seal of King Theodoric, or with the motto BONO ROMÆ (for the good of Rome). The lead sheets bore the names of various Popes, from Innocent III. (1130-1138) to Benedict XII. All these precious materials for the chronology and history of the basilica have disappeared, save a few planks from the roof, with which the doors of the modern church were made. Another sight must have struck the pilgrim as he first crossed the threshold, that of the "triumphal arch" between the nave and the transept, glistening with golden mosaics. We owe to Prof. A. L. Frothingham, Jr., of Baltimore, the knowledge of this work of art, he having found the description of it by cardinal Jacobacci in his book "De Concilio" (1538). The mosaics represented the emperor Constantine being presented by S. Peter to the Saviour, to whom he was offering a model of the basilica. It was destroyed, with the dedicatory inscription, in 1525.[83]