The walls were made of bricks, and the bricks were formed of clay and earth, which was dug from a trench made outside of the lines. This trench served the purpose of a ditch, to strengthen the fortification when the wall was completed. The water from the river, and from streams flowing toward the river, was admitted to these ditches on every side, and kept them always full. The sides of these ditches were lined with bricks too, which were made, like those of the walls, from the earth obtained from the excavations. They used for all this masonry a cement made from a species of bitumen, which was found in great quantities floating down one of the rivers which flowed into the Euphrates, in the neighborhood of Babylon. The River Euphrates itself flowed through the city. There was a breast-work or low wall along the banks of it on either side, with openings at the terminations of the streets leading to the water, and flights of steps to go down. These openings were secured by gates of brass, which, when closed, would prevent an enemy from gaining access to the city from the river. The great streets, which terminated thus at the river on one side, extended to the walls of the city on the other, and they were crossed by other streets at right angles to them. In the outer walls of the city, at the extremities of all these streets, were massive gates of brass, with hinges and frames of the same metal. There were a hundred of these gates in all. They were guarded by watch-towers on the walls above. The watch-towers were built on both the inner and outer faces of the wall, and the wall itself was so broad that there was room between these watch-towers for a chariot and four to drive and turn. The river, of course, divided the city into two parts. The king's palace was in the center of one of these divisions, within a vast circular inclosure, which contained the palace buildings, together with the spacious courts, and parks, and gardens pertaining to them. In the center of the other division was a corresponding inclosure, which contained the great temple of Belus. Here there was a very lofty tower, divided into eight separate towers, one above another, with a winding staircase to ascend to the summit. In the upper story was a sort of chapel, with a couch, and a table, and other furniture for use in the sacred ceremonies, all of gold. Above this, on the highest platform of all, was a grand observatory, where the Babylonian astrologers made their celestial observations.