National Geographic : 1933 Jan
©Aerial Explorations, Inc. UNCUT STONES CEMENTED WITH ADOBE FORM THE FORTS ALONG THEGREAT WALL Arial explorations, Inc. This stronghold, the largest discovered, is about 200 by 300 feet in extent, with rock breastworks 15 feet high (see text, page 82). Its location atthe top of a ridge permitted use of rolling bowlders against advancing foes. These military posts are invisible from the valley.