How about the unfinished city walls?

[ByzCat]

The picture with the pyramid and desert surroundings looks more like the walls decayed. If you look at the section of wall behind the coliseum there is a big dip in it but it doesn't continue to the bottom. If an invading army was blowing a hole in a wall they would go all the way through.

[N35t0r]

yeah, i was thinking that walls should be made obsolete...

I was actually thinking to make a mod of modern warfare with no walls, to encourage people to build fortresses and fortify units on hills and forests OUTSIDE cities, as it was done IRL for a long while.