The walls, as may be traced to-day, were thus divided. First, within was the great inner wall from 13½ to 15½ feet thick, which historians call τὸ κάστρον τὸ μέγα, τὸ μέγα τεῖχος. It rose probably about 50 feet above the ground, with a battlement of 4 feet 8 inches. It was guarded by ninety-six towers, standing about 180 feet apart, about 60 feet high, and projecting from the wall from 18 to 34 feet. These towers were distinct buildings from the wall, though connected with it. The capture of a tower would not necessarily involve the capture of the wall. From the roof of the tower the engineer discharged stones and Greek fire, and there, says Nicephorus Gregoras, the sentinels looked westward day and night, keeping themselves awake at night by shouting to one another along the line. Between the inner and outer walls was the inner terrace, ὁ περίβολος, in which were sheltered the troops for the defence of the outer walls. It was a space of from 50 to 64 feet. Above it rising now 10 feet, but probably of old nearly twice as far, was the outer wall, the "little wall." It is "from 2 to 6½ feet thick, rising some 10 feet above the present level of the peribolos, and about 27½ feet above the present level of the terrace between the outer wall and the moat."[63] The upper part is built above a lower solid portion, "for the most part in arches, faced on the outer side with hewn blocks of stone," and supported behind by arches which carried a parapet-wall. This wall was also protected by towers with small windows. Behind this outer wall the troops on which fell the brunt of the fighting, as in 1422 and 1453, were sheltered. Beyond the outer wall was an embankment or terrace, τὸ ἔξω παρατείχιον, some 60 feet broad. Then came the moat, of at least the same breadth as the terrace. This is now to a great extent filled up and used for market gardens, but in front of the Golden Gate it is still 22 feet deep. It had scarp and counter-scarp, each 5 feet thick, and the scarp was surmounted by a breast-work with battlements 5 feet high. Across the moat are walls, which were probably aqueducts. It seems probable that the moat itself was rarely if ever filled with water.