Your citadel should be properly protected with strong walls and arched gates. On every side such walls, with watch-towers on them standing close to one another, should be made as will admit six persons walking side by side on their top.
पुरं च ते सुगुप्तं स्याद् दृढप्राकारतोरणम्। अट्टाट्टालकसम्बाधं षट्पदं सर्वतोदिशम्॥