After Qin unified the six countries, political unity needed economic unity as the basis. Qin Shihuang followed the historical development trend and unified writing, weights and measures and currency. It is stipulated that "gold" is the upper currency, with it as the unit, with round square hole copper coins as the lower currency, and with half two as the unit. Qian Wen's "half Liang" is in line with the actual weight. As the main form of China currency, this square hole round money has been used for more than 2,000 years.

Why take this shape? Mainly ring-shaped, easy to carry, the square hole is not easy to rotate through the rope, which can prevent wear. Some people think that this form expresses the world outlook of ancient people. Square hole round coins in Qin Dynasty were the earliest official legal tender in the world.

To distinguish the "half-taels of money" between the Warring States and the Qin Dynasty, we can start with calligraphy. During the Warring States Period, Qian Wen's "Half Beam" was a big seal; In the Qin Dynasty, Qian Wen's "Half Liang" was a small seal. According to legend, Qin coins were cast by Prime Minister Lisi. Probably influenced by this, most of Qian Wen after Qin Dynasty came from dignitaries or calligraphers. There was also money for imperial books in the Song Dynasty.

One of the differences between Chinese ancient coins and western currencies is that the layout of Chinese ancient coins is mainly Qian Wen, and there are few patterns of circulating coins, while western currencies are mainly animals, plants, portraits and other patterns. The art of ancient money calligraphy is another topic.

It is said that in order to prevent the people from rebelling, Qin Shihuang collected weapons from all over the world and cast 12 gold men. This will inevitably affect the casting amount of copper coins. Due to the extremely high copper price and insufficient currency circulation, Qin Banliang's money is of high value. At the beginning of the Han Dynasty, the problem of "Qin money is more important than use" appeared. Han inherited the Qin system in a semi-literary style, but when Liu Bang became emperor, the country was very poor, and a lot of small money was cast instead, including "Yu pod half 28 baht half two, four baht half two, etc."

One or two is 24 baht, because Qin Banliang has lost a lot of weight, and half of it is not true. In particular, a kind of elm-like fruit called "Elm" weighs less than one gram and has a diameter of less than one centimeter. In the Han Dynasty, private minting was allowed, and coins were minted in counties, which led to currency disorder and inflation. Emperor Wu of the Han Dynasty made great changes to the monetary system.