Sentence:  Only paved alleyways tunneled through the <WSD>walls</WSD> of those fortresses into the mysterious core of intimacy behind the houses where backyards owned no fences , where one man 's property blended with the next to form courtyards in which no one knew privacy . 
Meaning of the word marked with <WSD> tags:  an architectural partition with a height and length greater than its thickness; used to divide or enclose an area or to support another structure