http://newscenter.lbl.gov/news-releases/2013/06/04/roman-concrete/
neat
Then again, the Romans didn’t pound their roads with thousands of cars, vans, and 18-wheelers on a daily basis. (all of them much heavier than chariots and animals along with imparting a much greater amount of force).
Subject an ancient Roman road to American style traffic and see how long it lasts.