Herodotus has a description of the famed Babylon,
"The city of Babylon is situated on a large plain. It is square in shape, and each side is fourteen miles long, so that the complete circuit is fifty-six miles. It is built like no other city known to the Greeks. A wide deep moat full of water runs round it, and inside the moat is a wall 330 feet high and 86 feet thick."
Walls, Moat and the making of Bricks
"I must tell you where the earth was used when it was taken from the moat, and how the wall was built. As they were digging the moat they formed the mud which was brought out of the excavations into bricks, and when they had molded a sufficient number of bricks, they baked them in kilns. With these bricks they built the banks of the moat, and after that the wall itself, using hot bitumen for mortar and inserting reed-mats every thirty rows to strengthen it. Along the edges on top of the wall they put one-roomed buildings facing each other, with sufficient space between them for a four-horse chariot to turn round. There are a hundred gates in the wall, all made of bronze with posts and lintels of the same material."
The City Grid
"The city itself contains many houses three or four stories high, and all the streets are straight, some running parallel to the river and some at right angles to it. At the end of each street which runs down to the river there is a gate made of bronze in the wall to give access to the river. These walls form the city’s outer defense. Inside them there is another wall, narrower than the first but almost as strong."
"The Euphrates, a wide, swift and deep river which rises in Armenia and flows into the Persian Gulf, runs through the city, dividing it into two parts. The wall runs down to the river on either side, and the ends are joined by fortifications of baked bricks along each bank of the river."
The Tower of ‘Bel’
"In each half of the city there is a fortified building; on one side of the river there is the royal palace with its great defensive wall, and on the other is the temple of Bel, the Babylonian Zeus. This is an enclosure a quarter of a mile square, with bronze gates, and was still in existence when I visited Babylon."
"In the middle of the enclosure is a solid square tower with its sides more than two hundred yards long. On top of it there is another tower, and another on top of that, and so on up to eight stages. The staircase to the upper stories runs spirally round the outside, and about halfway up there is a platform with seats where people going up can rest. On the top story there is a large temple in which there is a great couch covered with fine draperies, with a table made of gold alongside it."
Reference: Herodotus 484 - 425 BC, "Histories"