OntheninthdayoftheninthmonthintheChineselunarcalendar,peoplecelebratetheDoubleNinthFestival.Nineisayangnumber(atraditionalChinesespiritualconcept)inTheBookofChanges,soDoubleNinthiscalledChongyang.Climbingthemountainsisoneofthemostpopulartraditionsonthatday.InSeptembertheskyishighandtheairisfresh,andclimbingthemountainsishelpfultokeepphysicalfitness.Thetraditionofeatingdouble-ninthcakesisassociatedwithclimbingthemountains.Asakindoffestivalfoods,thedouble-ninthcakewasfirstusedtocelebratetheautumnharvest.Later,itdevelopedintothecustomofclimbingthemountainsandeatingdouble-ninthcakes,whichmeansthatourlifewillbecomebetterandbetter.Becausedoubleninthsoundslikelongevity(jiujiuinChinese),theDoubleNinthFestivalnowadayshasbeengivenanewmeaning-Seniors'Day.