Nerva was the last Emperor buried in the mausoleum of Augustus. Trajan’s ashes were laid to rest in an urn of gold under his monumental column. Hadrian determined to raise a new tomb for himself and his successors, and, like Augustus, selected a site on the green and shady banks of the Tiber, not on the city side, however, but in the gardens of Domitia, which, with those of Agrippina, formed a crown property called by Tacitus “Nero’s Gardens.” The mausoleum and the bridge which gave access to it were substantially finished in A.D. 136. Antoninus Pius, after completing the ornamental part in 139, transferred to it Hadrian’s ashes from their temporary burial-place in the former villa of Cicero at Puteoli, and was himself afterward interred there.
Beside the passages of the “Hadrian’s Life,” and of Dion Cassius, two descriptions of the monument have come down to us, one by Procopius, the other by Leo I. From these we learn that it was composed of a square basement of moderate height, each side of which measured 247 feet. It was faced with blocks of Parian marble, with pilasters at the corners, crowned by a capital. Above the pilasters were groups of men and horses in bronze, of admirable workmanship. The basement was protected around by a sidewalk and a railing of gilt bronze, supported by marble pillars crowned with gilded peacocks, two of which are in the Giardino della Pigna, in the Vatican. A grand circular mole, nearly a thousand feet in circumference, and also faced with blocks of Parian marble, stood on the square basement and supported in its turn a cone of earth covered with evergreens, like the mausoleum of Augustus.
Of this magnificent decoration nothing now re-mains except a few blocks of the coating of marable, on the east side of the quadrangle, near the Bastione di S. Giovanni. All that is visible of the ancient work from the outside are the blocks of peperino of the mole which once supported the outer casing. The rest, both above and below, is covered by the works of fortification constructed at various periods, from the time of Honorius (393403) to our own days. In no other monument of ancient and medieval Rome is our history written, molded, as it were, so vividly, as upon the battered remains of this castle-tomb. Within and around it took place all the fights for dominion with which popes, emperors, barons, barbarians, Romans, have distracted the city for fifteen hundred years.
Of the internal arrangement of the monument nothing was known until 1825, when the principal door was discovered in the middle of the square basement facing the bridge. It opens upon a corridor leading to a large niche, which, it is conjectured, contained a statue of Hadrian. The walls of this vestibule, by which modern visitors generally begin their inspection, are built of travertine, and bear evidence of having been paneled with Numidian marble. The pavement is of white mosaic. On the right side of this vestibule, near the niche, begins an inclined spiral way, 30 feet high and 11 feet wide, leading up to the central chamber, which is in the form of a Greek cross.
There is no doubt that the tomb was adorned with statues. Procopius distinctly says that, during the siege laid by the Goths to the castle in 537, many of them were hurled down from the battlements upon the assailants. On the strength of this passage topographers have been in the habit of attributing to the mausoleum all the works of statuary discovered in the neighborhood; like the Barberini Faun now in Munich, the exquisite statue of a River God described by Cassiano dal Pozzo, etc., as if such subjects were becoming a house of death. The mausoleum of Hadrian formed part of one of the largest and noblest cemeteries of ancient Rome, crossed by the Via Triumphalis. The tomb next in importance to it was the so-called “Meta,” or “sepulcrum Romuli,” or “sepulcrum Neronis,” a pyramid of great size, which stood on the site of the church of St. Maria Transpontina, and was destroyed by Alexander VI. in 1499.