Here is an excerpt from the http://www.survivalblog.com/
good article on home defense. I believe it is from another author but the references are there.
"Consider, on the other hand, a traditional home in North Africa. It presents a smooth, solid wall on four sides, broken only by a small and sturdy entrance onto the street. The entrance door leads through the house to an iron gate which blocks access to an inner courtyard. From the courtyard you can see an external staircase that goes up to the flat roof of the rooms surrounding the courtyard. This roof runs around the house and is bordered by a wall about chest height with a rounded edge.
Here we have an example of physical protection. The lack of external windows means an invader would have to scale a 15 foot wall to gain access. The rounded edge of the wall would prevent a grappling hook from getting a purchase and, in any event, a night watchman, stationed on the upper level, would immediately be aware of an assault. Down on the ground, the narrow door would prevent a large group of men from attacking the door altogether, while the inner gate would allow the residents to fight back against an armed attack. The upper level would also provide a firing point to defend all four quarters of the house. "