Winter Solstice, the shortest day of the year, falls on Dec. 21 or 22. In Chinese culture, it marks the beginning of deep winter and a break from farming in traditional agricultural society. It is also a time for family gatherings.

Northern China has maintained the tradition of eating dumplings on this day, while people in southern China eat tangyuan, or rice ball soup.

The Winter Solstice is among the 24 solar terms -- important astronomical points on the Chinese calendar -- to be listed by the UN Educational, Scientific, and Cultural Organization (UNESCO) as an Intangible Cultural Heritage of Humanity in late November.

Long queues were seen at noon outside many dumpling restaurants in Beijing, with some having to suspend delivery services because shops are so busy.

But few people know the origins of the custom. In northern China, people believe dumplings were invented by Zhang Zhongjing, a city governor dating back to the Han dynasty, some 1,800 years ago.

According to legend, on one cold winter day, while on his way back to Changsha in central China's Hunan province, Zhang saw many poor people suffering from cold and hunger. Some even had frostbitten ears. Feeling sympathetic, he made ear-shaped dumplings with lamb, chili pepper and other ingredients to keep them warm.

Winter Solstice, or Dongzhi, has been observed in China since the Shang Dynasty (1,600 - 1,046 B.C.), according to Liu Xiaofeng, a history professor at Tsinghua University. The 24 solar terms have guided farming in China for over 2,000 years.

Urbanization and modern agriculture have weakened the impact of solar terms on daily life, but cultural and dietary habits have been passed down from generation to generation