The festival began as early as the Warring States Period (475 - 221 BC)。 According to the yin/yang dichotomy that forms a basis to the Chinese world view， yin represents the elements of darkness and yang represents life and brightness。 The number nine is regarded as yang。 The ninth day of the ninth month is a double yang day， hence the name "Chong Yang Festival"。 (Chong means "repeat" in Chinese。) The ninth month also heralds the approach of winter。 It is a time when the living need warm clothing， and filial Chinese sons and daughters extended this to make the festival a time for providing winter clothes for their ancestors。 The Double Ninth Festival， therefore， also became an occasion to visit the graves of dead family members。 Clothes made of paper would then be burnt as offerings。