The Hippodrome was now completed,[126] to become “the axis of the Byzantine world,” and there, in addition to other monuments, the Serpent Column from Delphi was placed. The adjoining Thermæ of Zeuxippus were improved.[127] An Imperial Palace,[128] with its main entrance on the southern side of the Augustaion, was built to the east of the Hippodrome, where it stood related to the race-course very much as the Palace of the Cæsars on the Palatine was related to the Circus Maximus. There, at the same time, it commanded the beautiful view presented by the Sea of Marmora, the Prince’s Islands, the hilly Asiatic coast, and the snow-capped Bythinian Olympus. Eusebius, who saw the palace in its glory, describes it as “most magnificent;”[129] while Zosimus speaks of it as scarcely inferior to the Imperial Residence in Rome.[130] On the eastern side of the Augustaion rose the Basilica,[131] where the Senate held its principal meetings. It was entered through a porch supported by six splendid columns of marble, and the building itself was decorated with every possible variety of the same material. There also statues of rare workmanship were placed, such as the Group of the Muses from Helicon, the statue of Zeus from Dodona, and that of Pallas from Lindus.[132] According to Eusebius, Constantine adorned the city and its suburbs with many churches,[133] the most prominent of them being the Church of Irene[134] and the Church of the Apostles.[135] The former was situated a short distance to the north of the Augustaion, and there, as restored first by Justinian the Great, and later by Leo III., it still stands within the Seraglio enclosure, now an arsenal of Turkish arms. The Church of the Apostles, with its roof covered with tiles of gilded bronze, crowned the summit of the Fourth Hill, where it has been replaced by the Mosque of the Turkish Conqueror of the city. There, also, Constantine erected for himself a mausoleum, surrounded by twelve pillars after the number of the Apostles;[136] and in the porticoes and chapels beside the church most of Constantine’s successors and their empresses, as well as the patriarchs of the city, found their last resting-place in sarcophagi of porphyry or marble. Whether Constantine had any part in the erection of St. Sophia is extremely uncertain. Eusebius is silent regarding that church; Socrates ascribes it to Constantius. Possibly Constantine laid the foundations of the famous sanctuary.