Pax romana was so revolutionary, that i'd have to go Roman. Imagine being able to travel from place to place on an actual road with relatuve safety thanks to the good ol' roman military. And, a lot of Roman architecture had more practical uses, like the famous aqueducts and the Coliseum was used as a stadium where people filled the seats. Most ancient empires' great works of architecture were usually just religious temples, where only the god-priest-zealot dudes could go. I just find Rome to be the least ooga-chaka of the ancient civilizations, probably because it came later than most.