The citizens of Constantinople found their principal recreation in the chariot-races held in the Hippodrome, now the At Meidan, to the west of the mosque of Sultan Ahmed. So much did the race-course (begun by Severus but completed by Constantine) enter into the life of the people that it has been styled "the axis of the Byzantine world." It was not only the scene of amusement, but on account of its ample accommodation it was also the arena of much of the political life of the city. The factions, which usually contended there in sport, often gathered there in party strife. There emperors were acclaimed or insulted; there military triumphs were celebrated; there criminals were executed, and there martyrs were burned at the stake. Three monuments remain to mark the line of the Spina, around which the chariots whirled; an Egyptian obelisk of Thothmes III., on a pedestal covered with bas-reliefs representing Theodosius I., the empress Galla, and his sons Arcadius and Honorius, presiding at scenes in the Hippodrome; the triple serpent column, which stood originally at Delphi, to commemorate the victory of Plataea 479 B.C.; a lofty pile of masonry, built in the form of an obelisk, and once covered with plates of gilded bronze. Under the Turkish buildings along the western side of the arena, some arches against which seats for the spectators were built are still visible. The city was supplied with water mainly from two sources; from the streams immediately to the west, and from the springs and rain impounded in reservoirs in the forest of Belgrade, to the north-west, very much on the system followed by the Turks. The water was conveyed by aqueducts, concealed below the surface, except when crossing a valley. Within the city the water was stored in covered cisterns, or in large open reservoirs. The aqueduct of Justinian, the Crooked aqueduct, in the open country, and the aqueduct of Valens that spans the valley between the 4th and 3rd hills of the city, still carry on their beneficent work, and afford evidence of the attention given to the water-supply of the capital during the Byzantine period. The cistern of Arcadius, to the rear of the mosque of Sultan Selim (having, it has been estimated, a capacity of 6,571,720 cubic ft. of water), the cistern of Aspar, a short distance to the east of the Gate of Adrianople, and the cistern of Mokius, on the 7th hill, are specimens of the open reservoirs within the city walls. The cistern of Bin Bir Derek (cistern of Illus) with its 224 columns, each built up with three shafts, and the cistern Yen Batan Serai (Cisterna Basilica) with its 420 columns show what covered cisterns were, on a grand scale. The latter is still in use.[1]