Each tower had a chamber on the level of the peribolos, provided with small windows. The lower portion of most of the towers was generally a solid substructure; but in the case of square towers it was often a small chamber reached from the Outer Terrace through a small postern, and leading to a subterranean passage running towards the city. These passages may either have permitted secret communication with different parts of the fortifications, or formed channels in which water-pipes were laid. Notwithstanding the comparative inferiority of the Outer Wall, it was an important line of defence, for it sheltered the troops which engaged the enemy at close quarters. Both in the siege of 1422,[200] and in that of 1453,[201] the most desperate fighting occurred here. The Outer Terrace. Τὸ ἔξω παρατείχιον.[202] The embankment or terrace between the Outer Wall and the Moat is some 61 feet broad. While affording room for the action of troops under cover of the battlement upon the scarp of the Moat,[203] its chief function was to widen the distance between the besiegers and the besieged. The Moat. Τάφρος: σοῦδα.[204] The Moat is over 61 feet wide. Its original depth, which doubtless varied with the character of the ground it traversed, cannot be determined until excavations are allowed, for the market-gardens and _débris_ which now occupy it have raised the level of the bed. In front of the Golden Gate, where it was probably always deepest, on account of the importance of that entrance, its depth is still 22 feet. The masonry of the scarp and counterscarp is 5 feet thick, and was supported by buttresses to withstand the pressure of the elevated ground on either side of the Moat. The battlement upon the scarp formed a breastwork about 6-½ feet high. At several points along its course the Moat is crossed by low walls, dividing it into so many sections or compartments. They are generally opposite a tower of the Outer or Inner Wall, and taper from the base to a sharp edge along the summit, to prevent their being used as bridges by an enemy. On their southern side, where the ground falls away, they are supported by buttresses. Dr. Paspates[205] was the first to call attention to these structures, and to him, also, belongs the credit of having thrown some light upon their use. They were, in his opinion, aqueducts, and dams or batardeaux, by means of which water was conveyed to the Moat, and kept in position there. But this service, Dr. Paspates believed, was performed by them only in case of a siege, when they were broken open, and allowed to run into the Moat. At other times, when no hostile attack was apprehended, they carried water across the Moat into the city, for the supply of the ordinary needs of the population.