After the unification of the six countries, Qin Shihuang decided to abolish the old coins of the six countries in the Warring States, and improved them on the basis of the Qin Banliang coins in the Warring States, forming a Qin Banliang coin with a round square hole. This currency spread all over the country, ending the state of different forms and different weights of money since the pre-Qin period.
Qin Banliang's design embodies a high level of technology. Its outer circle has no inner and outer contours, and its back is flat. The character "Banliang" in the seal script is located at the tooth holes on both sides of the excircle, and the Qian Wen is prominent, which shows the high standard and strict requirements of Qin State's coinage. The appearance of Qin Banliang not only marked the unification of China's currency, but also had an important influence on the form of coins in later generations, and established the circular square hole as the basic form of ancient currency in China. This tradition lasted for more than two thousand years.
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In 22 1 BC, Qin Shihuang destroyed six countries and established the first unified autocratic and centralized feudal regime in history. In order to eliminate the remnants of the warlord regime and consolidate the unity of the country, Qin Shihuang unified the written language and measurement, and at the same time carried out a big move to unify the currency. In fact, unifying the currency is to spread the original currency of Qin to the whole country and abolish the currency of the six governors. According to Records of Historical Records, PingZhun Book:
In the Qin Dynasty, the currency of a country in China was third-class, and gold was named as the superior currency; Copper coins, commonly known as half a tael, are as heavy as the text, and are the next coins. Jade beads, tortoiseshell, silver and tin are ornaments, not coins. However, each one is changeable at any time.
Except for the last sentence, this passage is probably narrated by Sima Qian according to the imperial edict of Qin Shihuang in Ji Qin, but it is puzzling. The article says: "A country's currency is third-class", but it seems contradictory to talk only about second-class gold and copper coins.
The above contents refer to Baidu Encyclopedia-Qin Coin.