Symbolism, Imagery, Allegory
The narrator spends so long talking about the wall around his schoolhouse that we’re bound to sit up and take notice. Walls and gates tend to make us feel trapped. And indeed, “William Wilson” is the story of a man who is trapped – psychologically – by his conscience (if you choose to interpret the story this way, and of course you don’t have to). William flees all over the world and cannot escape his double, so in a sense he is trapped by his double’s insistence that he behave morally.