Some of the older topographers had conjectured that the ruins in the Colonna Gardens, wrongly, as has been shown, ascribed to Aurelian’s Temple of the Sun, and also the massive substructions and stairs which have been found behind the stables of the Quirinal Palace on the west slope of the hill, belonged to the Thermæ of Constantine. This conjecture has been revived and ingeniously supported by Professor Reber, who remarks that the outer court of the Thermæ, to judge by the extent of that of the baths of Diocletian or of Caracalla, may very well have reached across the whole breadth of the hill from east to west, and further that the approach to the Thermæ would naturally be placed on the west side, where the Imperial fora lay. If so, the building called the tower of Mæcenas stood exactly in the position at the summit of the colossal flight of stairs now hidden under the Papal stables which would answer to the entrance portico of the Thermæ. The fragments of the so-called Tower of Mæcenas are very similar to those of the portico of Octavia, which was also the entrance to a grand enclosure. They consist of two huge blocks of marble, the largest of which is seventeen feet in length, ornamented with mouldings of the usual Corinthian character, and with a frieze beautifully decorated with festoons of foliage enclosing birds and genii. The style is of a late epoch, and might very probably belong to the Constantinian age. CHAPTER V. THE VELABRUM AND THE CIRCUS FLAMINIUS. [Sidenote: Janus Quadrifrons.]