At every military base in Iraq, and I'd suspect, Afghanistan, you see giant monoliths called T-Walls. T-Walls provide two services: protect and contain. Which one it does is entirely dependent on which side of the wall you're on.
You've seen T-Walls too, everytime you drive through a construction zone. They're much shorter, and typically wider, and go by the moniker 'concrete barriers.' Their purpose is exactly the same - they protect the workers on the other side, and contain whatever mayhem traffic may cause in the thru lanes.
Are they protecting us from traffic in Iraq? Hardly. Their job is to protect us from most types of lobbed or rocketed munitions. Could be mortars, could be grenades, could be rocket powered grenades (RPG's). They're typically placed around the perimeter of most buildings, and around the pods that consist of the trailers we live in.
That being said, it's all a crap shoot as to whether you're on the protect or contain side.
As I look out the window of my room, I see an 8' high T-wall. Beyond the wall is a gravel road about 30' across. Good, I'm protected, right? Well, if an explosive happens to land in that roadway, yep, I'm protected, and the blast is contained. BUT, what if that same munition happens to land in that 4' space between my trailer and the T-Wall? *BOOM!* All of a sudden, I'm on the containment side, and anyone in the road would be protected.
Like I said, it's a crap shoot. Still, they do provide a sense of protection, that that goes a long way towards our peace of mind, even if they do block the view.