This pen-and-ink drawing depicts a parapet, common in Middle Eastern architecture.  Essentially, what a parapet is, is a wall surrounding a balcony, terrace, or roof, that serves as a fortified railing.  These solid railings were originally designed for protection, as they can be used defensively in case of attack.  Parapets are most often associated with the Middle East, but this architectural design feature is used all over the world. Click here to enlarge.