The essays presented in this volume describe a phenomenon so widespread in human time and space that its importance is easily overlooked. City walls shaped the history of warfare; the mobilization of manpower and resources needed to build them favored some kinds of polities over others; and their massive strength, appropriately ornamented, created a visual language of authority. Previous collective volumes on the subject have dealt mainly with Europe, but the historians and art historians who collaborate here follow a comparative agenda. The millennial practice of wall building that branched out from the ancient Near East into India, Europe, and North Africa shows continuities and points of contact of which the makers of urban fortifications were scarcely aware; separate traditions in China, sub-Saharan Africa, and North America illustrate universal themes of defensive strategy and the symbolism of power, each time embedded in a distinctive local context.