Actually, I was thinking about giving that as an example, but I did not. I think they were using it because measurements were unrealiable and switched alot, but everyone can imagine how big 4 chariots are.
In short, I think it was a boast [look how big our walls are] rather than a -
"Are you tired of being the same old footsore sentry? Forget about defending the Egyptians, come over to Babylon and patrol walls in style, with your own chariot!"
Yeah, I really don't think the Babylonians used chariots on their walls. I have never historically heard of any reference to mounted units on walls. But I can imagine monsters, etc up there.