Further, I must relate where the earth was used as it was dug from the moat and how the wall was constructed. As they dug the moat, they made bricks of the earth which was carried out of the place they dug, and when they had moulded bricks enough, they baked them in ovens; then using hot bitumen for cement and interposing layers of wattled reeds at every thirtieth course of bricks, they built first the border of the moat and then the wall itself in the same fashion. On the top, along the edges of the wall, they built houses of a single room, facing each other, with space enough between to drive a four-horse chariot. There are a hundred gates in the circuit of the wall, all of bronze, with posts and lintels of the same. There is another city, called Is, eight days' journey from Babylon , where there is a little river, also named Is, a tributary of the Euphrates river ; from the source of this river Is, many lumps of bitumen rise with the water; and from there the bitumen was brought for the wall of Babylon .