This charming Han dynasty (206 b.c.- 220 a.d.) ink stone, modeled in the form of a turtle, features "the eight trigrams" pa-kua carved into the top of its removable shell. The eight trigrams are among the earliest and best-known images associated with Taoism. These visual symbols are the basis for the sixty-four hexagrams of the ancient divination text, the I-Ching or The Book of Changes which was formulated during Western Chou (1050-772 b.c.). In addition to divination, the eight trigrams played a vital role in Taoist alchemical practices and helped explain the cosmological principles of transformation. The eight trigrams and their symbolism are one of several Bronze Age traditions that coalesced during Han to form the basis of religious Taoism.