None of the Roman emperors had so great a passion for building as Hadrian, who succeeded Trajan A.D. 117. He erected a vast number of edifices, and in his reign Rome attained its greatest height of architectural splendor. The most remarkable among the edifices which he built was the Temple of Venus and Rome, facing on one side the Colosseum, and the other the Forum, on the site of the Atrium, or the golden house of Nero. This seems to have been one of the largest of the Roman temples, erected on an artificial terrace five hundred feet long and three hundred broad. It was surrounded with a portico four hundred feet by two hundred, and another portico of four hundred columns inclosed the terrace on which the temple was built, the columns of which were forty feet in height. The roof was covered with bronze tiles. Ammianus Marcellinus classes this magnificent temple with the Capitoline Temple, the Flavian Amphitheatre, and the Pantheon. The next greatest work of Hadrian was the Mausoleum, which is now converted into the Castle of St. Angelo, built on a platform of which each side was two hundred and fifty-three feet in length. From the magnificent colonnade which supported the platform on which it was built, and the successive stories supported by arches and pillars, between which were celebrated statues, this circular edifice, one hundred and eighty-eight feet in diameter, must have been one of the most imposing edifices in the city. After eighteen centuries, it still remains a monument of architectural strength, and it served for one of the strongest fortresses in Italy during the Middle Ages. I pass by, without notice, the villa this emperor erected at Tivoli, the ruins of which are among the most interesting which remain of that great age. [Sidenote: Column of Marcus Aurelius.] [Sidenote: Arch of Septimius Severus.] [Sidenote: Baths of Caracalla.]