The festival is based on the theory of Yin-yang, the two opposing principles in nature. In an ancient and mysterious book Yi Jing, or The Book of Changes, number "6" was thought to be of Yin character, meaning feminine or negative, while number "9" was thought to be Yang, meaning masculine or positive. The ninth day of the ninth lunar month is a day when the two Yang numbers meet. So it is called Chongyang. Chong means double in Chinese. Also, as double ninth was pronounced the same as the word to signify "forever", both are "Jiu Jiu," the Chinese ancestors considered it an auspicious day worth celebration. That's why Chongyang has been an important festival since ancient times.
The festival is held in the golden season of autumn, at harvest -time. The brght clear weather and the joy of bringing in the harvest make for a festive happy atmosphere.The Double Ninth Festival is usually perfect for outdoor activities. Many people go hiking and climbing in the country, enjoying Mother Nature's final burst of color before she puts on her dull winter cloak. Some will carry a spray of dogwood. The dogwood is a plant with a strong fragrance, and is often used as a Chinese herbal medicine. People in ancient times believed it could drive away evil spirits and prevent one from getting a chill in lalte autumn.
It is hard to say when these customs were created. But there are many stories which are closely related. The book Xu Qi Xie Ji ,written by Wu Jun in the sixth century has one such story.
In ancient times, there lived a man named Huan Jing. He was learning the magic arts from Fei Changfang, who had become an immortal after many years of practicing Taoism. When the two were climbing a mountain one day, Fei Changfang suddenly told Huan Jing that On the ninth day of the ninth month, disaster will come to his hometown and in order to avoid the disaster, he must go home immediately, make a red bag for each family members and put a spray of dogwood in every one, all drink some chrysanthemum wine and tie the bags to their arms, then leave home quickly and climb to the top of a mountain. Later, Huan Jing and his family escaped disaster by following Fei Changfang's instructions.
And so hill-climbing, drinking chrysanthemum wine, hanging dogwood sprays and other customs handed down from the Han dynasty story of Huan Ching and Fei Chang-fang became the traditional activities of the Chong-yang Festival to avoid disaster and danger.
Today the custom of ascending a height was passed down. Therefore, the Double Ninth Festival is also called "Height Ascending Festival". The height people will reach is usually a mountain or a tower. On this day, people also will eat Double Ninth Gao (or Cake). In Chinese, gao (cake) has the same pronunciation with gao (height). People do so just to hope progress in everything they are engaged in. There is no fixed ways for the Double Ninth Cake, but super cakes will have as many as nine layers, looking like a tower.