According to Herodotus who apparently saw them, the walls were the equivalent of 85 feet thick.
It's problematic to presume a figurative or purely symbolic meaning for Biblical passages unless context indicates a figurative or symbolic use. As far as the sun being darkened and the moon being red, there are numerous, legitimate, known potential causes for that. Volcanic eruptions can do it, asteroid impact, even a large forest fire. I've seen the moon visibly reddened by smoke from a forest fire myself, although I doubt it was to the highly noteworthy degree of prophecy. It would be a very major occurrence.
Clearly, it's meant literally.
your right, I could have sworn thats what I read. Oh well next time through the Bible, my examples will be better.
Maybe it was that Babylons walls were never destroyed as the city fell easily in one day.....?
In 538 B.C.E., Cyrus invaded Babylonia. A battle was fought at Opis in the month of June, where the Babylonians were defeated; and immediately afterwards Sippara surrendered to the invader. Nabonidus fled to Babylon, where Gobryas pursued him, and on the sixteenth of Tammuz, two days after the capture of Sippara, “the soldiers of Cyrus entered Babylon without fighting.”
http://www.newworldencyclopedia.org/entry/Babylonian_Empire
I knew I had it right, well almost!