Ok, looks to me like: 1. you don't have ANY light source inside the room. 2. you have the ambience up a bit on the material you're using which is helping to cause the loss of definition you're seeing. 3. the only light is the sun ...maybe? Make a couple of radial lights and put them up by the ceiling. Space them in a row midway between the two rows of columns...so kinda of middle of the roomish, use maybe three or four. Turn the intensity on those lights down to about 4 - 7 max. Then on the marble material turn ambience all the way off. See what that looks like.