A cash is a round coin with a square hole in the middle. The coin bears symbols that indicate its weight and the issuing authority. Such cash coins were cast in China for more than 2000 years. They were a perfect symbol of imperial authority. Both – the emperor and the coin – connected heaven and earth, yin and yang. The Chinese thought of the sky as a kind of dome that was allegorized by a circle. The world, however, was flat and symbolized by a square. The task of each emperor was to safeguard peace between heaven and earth, and to request good crops and prosperity from the Heavenly Emperor. The imperial coins took up this symbolism – they were round with a square hole. In this way the cash coins, the major Chinese money until the 19th century, reflected Chinese worldview perfectly.