The QSM Software Almanac is an invaluable resource. It establishes a norm for software projects, including best of class, worst of class and averages. In addition, it profiles the state of the art of software construction and enhancement. I wish I'd had this wonderful reference book years ago.
From the exterior face of the wall towers must be projected, from which an approaching enemy may be annoyed by weapons, from the embrasures of those towers, right and left.