A 2000 year old city has a much better chance of being walkable than an American city. Take a look at something like the Dallas/Fort Worth area. It’s an enormous sprawling web of low density suburbs. To make it walkable would require a very large amount of effort and that effort would likely be wasted due to the climate. Even a five minute walk down the street is going to leave you exhausted and dripping with sweat on most summer days there.