September 9th of the lunar calendar is the traditional Double Ninth Festival (Chongyang Festival). In the ancient book “Yijing”, "six" is defined as the Yin number, and "Nine" as the Yang number. On September 9th, the sun and the moon merge with each other, so it is called Chongyang, meaning sun and moon merged. It also known as Chongjiu (double ninth). The ancients thought it was a auspicious day to celebrate, and they began to celebrate this festival from a very early age.
On this day, people also have the custom of eating "Chongyang cake". In Chinese, "high" is homonymous with "cake". People will use "Chigao" instead of "Denggao" to wish all things high. Chongyang cake, also known as flower cake, chrysanthemum cake and five color cake, has no definite method of making and is more casual. The highest one has nine stories, like a tower.