A solid citadel starts with the right stones. Layer a thick outer wall of hard, weather‑resistant granite to keep the battering at bay, then back it with a middle course of softer limestone that can absorb shock without cracking. Finally, tuck a thin inner lining of lime mortar or a damp‑proof stone into the core to seal any gaps. This three‑tiered approach gives the wall mass, shock absorption, and a last line of defense against tunnellers or sappers. Add a sloping parapet on the outer face to deflect arrows, and a small, hidden drainage channel in the base to keep water from seeping in. That way, the enemy faces a wall that is both an artful monument and a fortress that demands careful planning to breach.