Apparently the Israelis don't understand how walls work...
I stopped watching the movie after Jerusalem was overrun, because it's just so breathtakingly stupid.
Let me summarize the steps on how walls work:
Step 1: Build a big *beep* barrier which is hard to cross
Step 2: GUARD that barrier, so you can kill anyone who tries to cross it while they are vulnerable due to having to cross that barrier.
Not exactly rocket science.
This is why every historical wall you see has guard towers and space for people to stand on top of it - because the wall is absolutely useless without them - as the Israelis discovered when the Zombies easily piled on top of each other and crossed it, because they had nobody guarding it to shoot them down as they climbed.
So they are capable of building a huge wall in record time, but not of understanding why you build walls in the first place. Yeah, that's the sort of thing that just kills a movie.