Historically, linguistic signs have been—and remain—the greatest and most complete semiotic system created by human beings. Volume 8 of Huainanzi (《淮南子》) describes the origin of written language. When Cang Jie created Chinese characters, there came millets from the sky and ghosts cried at night. Zhang Yanyuan of the Tang Dynasty explained the origin of written language like the following. Cang Jie had four eyes to look at the celestial phenomena. According to the patterns of the tortoises, he created the Chinese characters then.