Qingming Festival, also called “Tomb Sweeping Day” or "Cold Food Day", is the most important day for people to offer sacrifice to ancestors. On the day of tomb sweeping, the descendants would clear the wild grass around the ancestor's tomb, clean the dust, and then present the food and fresh flowers.
It started from the Zhou Dynasty, with a history of over 2500 years. Qingming is one of the 24 solar terms in China, indicating the coming of late spring, thus the best plowing and growing time.
Since people with weak constitutions might get hurt by eating cold raw food on Qingming, when the weather is still cold, various activities were invented for body-building, like stepping-the-green outgoing, swing, Chinese football, polo, willow-planting, tug-of-war, and rooster-fighting, etc.
"Stepping-the-green" refers to the spring-outgoing people talk about now. Qingming is in early March when it begins to turn warm, and everything is blooming. So it is just a good time to go out for a walk. And so Qingming is not just a blue time for remembrance, but also a green time for fun.
Since the ancient times, there have been a lot of works of art and poems about Qingming, manifesting the emphasis and passing-on of the Chinese people on Qingming. Of these, Tomb Sweeping Day by Du Mu in the Tang Dynasty is a poem of household fame.