The upcoming post-apocalyptic war movie Wynter Dark has released a few concept designs of New York city 800 years in the future, during our next ice age. Looks like Lady Liberty is still standing (as usual in post-apocalyptic movies), but everything else is frozen and desolate. It also appears that the citizens of NYC have constructed some sort of barrier, obviously to keep their enemies from across the pond out of their city. There are no more details other than that out there for the moment on this 20th Century Fox film, but click through for a look at a snow-tank of the future.
@Gann: I guess, alternately it could be a people with advanced science, but not much imagination. So, they have robots that could built some kind of awesome roving antipersonnel cannons, or something, but all they can think of is, "Uh, uh....a giant wall!"
@kwizhader: Less eco-conscious so much that I was assuming that, post-apocalypse, our major manufacturing concerns wouldn't be operating at peak efficiency. If we wanted to build a wall, we'd need to use what was lying around.