Time: 539 BC
178. Cyrus, so soon as he had made subject to himself all other parts of the mainland, proceeded to attack the Assyrians. Now Assyria has doubtless many other great cities, but the most famous and the strongest, and the place where the seat of their monarchy had been established after Nineveh was destroyed, was Babylon; which was a city such as I shall say.–It lies in a great plain, and in size it is such that each face measures one hundred and twenty furlongs, the shape of the whole being square; thus the furlongs of the circuit of the city amount in all to four hundred and eighty. Such is the size of the city of Babylon, and it had magnificence greater than all other cities of which we have knowledge. First there runs round it a trench deep and broad and full of water; then a wall fifty royal cubits in thickness and two hundred cubits in height: now the royal cubit is larger by three fingers than the common cubit.
– Herodotus, Book 1
Pictured: panoramic view of ruins of city. Larger picture.
Furlong = 1/8 of a mile. 120 furlongs = 15 miles.
Royal Cubit = 20.6 inches. Wall was 86 feet thick and 343 feet high. (A football field is 300 feet goal to goal.)