I agree with the others about the marble. It looks nice. And it makes the center seem like it's intentionally not a part of the physical plane of the map, rather than unintentionally so, which is a good thing.
I'm not sure that the broken chariot works for me. The idea does, but I couldn't tell what the picture was supposed to be until I read your description of it. Also, is it just me, or does everyone seem to be in the inner lanes, and hardly anyone in the outer ones?
If you wanted to do any more editing on the crowd -- and I'm not saying you necessarily need to -- then you might look into shifting the colors to ones that are more setting-appropriate. I'm guessing that bright blues and yellows were probably less common as clothing colors back then, compared to whites, greys, and browns. Also, most spectators were probably dark-haired and bare-headed.
Oh, and I still can't officially condone Julian :) But I suppose K would actually be worse, which would mean having to jump from I to L. Hrm. (Hey, speaking of which... if "counterclockwise" doesn't have a U, should it really have a K?)