Currency Museum Bank of Japan
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FAQ currency

Q2. Why did old Japanese coins have a square hole in the middle?

A2. The origin of a square hole in the middle of round coins can be traced back to the half-tael circular coin, which was issued in the third century B.C. by Qin Shi Huang, the First Emperor of China's Qin Dynasty. In China, circular and square shapes symbolize the sky and the earth, respectively, and the coin was considered good luck since it combined the two shapes. In the final stage of the minting process, a square bar was passed through the hole to make it easier to polish the sides of the coin.

Similar types of coins -- circular coins with a square hole in the middle -- spread across East Asia, and in Japan they were used for more than 1,000 years.