Origin of the legend 1. Copper coins with square holes correspond to the theory that the sky is round and the earth is square. In ancient times, people believed that the sky was round and the earth was square, so Qin Shihuang made coins based on this model. 2. Easy to carry. Coil the coins and wrap them around your waist. It is both convenient and safe to carry. This is the origin of the word "travel". "Travel expenses" refers to travel expenses today. But why are travel expenses so costly and troublesome? Coiled and entangled are synonyms. Of course money, coiled and entangled have nothing to do with each other today, but there was some inevitable connection in ancient times! Ancient coins are metal coins with a hole in the middle. A thousand coins are often hung up in strings with ropes. The rope through which the coins are threaded is called "Guan", so a thousand coins are also called a hanging coin or a consistent coin. There is a play called "Fifteen Strings of Money", which is a case involving fifteen strings of money. Not to mention that there were no travellers' checks and credit cards in ancient times, even banknotes only came later. Therefore, when people traveled far away for business and to visit relatives, they could only bring bulky bunches of copper coins with them. Wrapping up copper coins and wrapping them around your waist is both convenient for carrying and patrolling. Therefore, the ancients called this "coiled" and "wrapped" travel expenses "coiled". 3. There is a principle in being a human being. Copper coins are round on the outside and square on the inside. The same is true for being a human being. Be smooth in doing things, but keep a square heart. 4. After the coins are cast, use a square drill to insert them into the holes for easy polishing. The extended meaning is: to unify the currencies of previous countries, making transactions more convenient and simple, and does not involve currency conversion. It is worth mentioning that after the Qin Dynasty, the The coins of more than a thousand years, except for the coins made by Wang Mang who practiced swordsmanship at one time, all have a square hole in the middle