An old city wall stands for collective protection and the line between inside and outside. Dream books read it as the defences that make you feel safe, or keep you apart.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.