The other obelisk is composed of several pieces of stone, and seems, by many cavities between the stones, to have been covered with brass plates; which, together with its height, must have rendered it superior to the former in magnificence. Between these obelisks is the Delphic pillar. The aqueduct of the Roman emperors still remains[163]. It was first erected by Hadrian: it was called by his name; subsequently it bore that of Valens, and of Theodosius. Being ruined by the Avans in the reign of Heraclius, it was repaired by one of the Constantines. In a later period Solyman, called the Magnificent, finding it gone to decay, caused it to be restored. It consists of a double line of arches, built with alternate layers of stone and brick. Within the walls of Constantinople[164] the Greek emperors had formed, by excavation, a number of immense cisterns, or reservoirs, which were always to be kept full, and which might supply the capital in case of siege. One of them, though no longer performing the office for which it was intended, is still one of the curiosities of Constantinople, to which all travellers are conducted. It is a vast subterranean edifice, whose roof is supported by an immense number of columns, each column being curiously formed of three pillars placed one on the top of the other. The Turks call it the place of the "thousand and one columns"--not that the columns are really so numerous--but because it is the favourite number of the oriental nations. Though the earth has, in part, filled it up, it is still of great depth. The whole cavity, according to Dr. Walsh, is capable of containing 1,237,939 cubit feet of water when full. It is now, however, dry; and a number of silk-twisters have taken possession of it, and ply their trade at the bottom in almost utter darkness. There is another, also, which still exists as a cistern; which Dr. Walsh, who first gave us any account of it, describes as being a subterraneous lake, extending under several streets, with an arched roof that covers and conceals it, supported on three hundred and thirty-six magnificent pillars. Some remains of a large antique structure are seen on the side of the Hippodrome; and it has been conjectured that this was the palace of the emperors; others suppose it to have been part of the Basilica, the form of which Gyllius believes to have been quadrangular; in opposition to those who had described it as an octagon. The Basilica was a college for the instruction of youth. In the reign of Basilicus there happened a great fire, and which consuming whole streets, with many stately edifices, wholly destroyed the Basilica, together with its library, containing six hundred thousand volumes. Amongst these curiosities there was a MS. of the Iliad and Odyssey, written in letters of gold; upon a serpents gut, one hundred and twenty feet in length.