This coin, which has influenced China for more than 1000 years, is "Kaiyuan Bao Tong". After Qin Shihuang unified the six countries, he thought that coins should also be unified, which was the real unification. At that time, people thought that the sky was round and the earth was square. So I invented "Qin Banliang" with a square hole on it, which is ancient money.

Later, in the Sui Dynasty, people began to make coins privately, and the coins made were far lower than the original ones. Coins are different in size and weight all over the country, so different coins can't be used again. In the Tang Dynasty, the original currency officially stopped circulating, and the "Kaiyuan Bao Tong" with a diameter of 2.2 cm -2.6 cm and a weight of 4.5 g -5 g was issued. At this time, the shape of coins began to become symbolic and abstract.

In addition, many people think that Bao Tong in Kaiyuan represents the number of years. Because Xuanzong of the Tang Dynasty had the title of Kaiyuan, this statement is very wrong. Kaiyuan Bao Tong was created in the early Tang Dynasty, and the word was put forward by Ou Yangxun. Ou Yangxun came from the early Tang Dynasty, but Xuanzong was born in the prosperous Tang Dynasty. The age difference between them is one hundred years, so Kaiyuan Bao Tong can't be the representative year number.

Since then, Kaiyuan Bao Tong has been used in all places ruled by the Tang Dynasty. Later, the Tang Dynasty died in 907 AD. After the demise of the Tang Dynasty, people still used Kaiyuan Bao Tong as the coin, but at this time, Kaiyuan Bao Tong made in different places was different. Kaiyuan Bao Tong was still used and manufactured in Song Dynasty, and was also widely used in Guangdong and Guangxi in Qing Dynasty. It was not until the Republic of China that Kaiyuan Bao Tong slowly withdrew from the historical stage.