On July 1, 1921 the Board of the China Aviation of the Peking Government organized the Peking-Shanghai Aviation line. The Peking-Tsinan section was the first opened to traffic, marking the beginning of the postal air mail service in China. The first set of air mail stamps issued for this occasion consists of five denominations valued from 15 to 90 cents, which have for their central design a biplane flying above the Great Wall with the five-colored national flag painted on its rudder. These stamps are commonly known as〝Air Mail Stamps of the First Issue.〞