February 11 is National Foundation Day, a national holiday for Japanese people to remind themselves of the nation's founding and foster their love for the nation.
Japan switched from the traditional Japanese calendar - a lunar calendar based on the waxing and waning of the moon - to the Gregorian calendar starting in January 1873. It was at this time that the day of the enthronement of Emperor Jinmu, the first Japanese emperor, was made a national holiday and named Kigen-setsu. February 11 was determined as the day of enthronement by calculating the date in the solar calendar corresponding to the date recorded in the Nihon Shoki (The Chronicles of Japan), Japan's first history compiled on imperial orders. (However, many historians believe that Emperor Jinmu's enthronement, as described in the Nihon Shoki, was not a historical fact but folklore.)
Before World War II government offices and schools throughout Japan held all sorts of celebrations on Kigen-setsu, but after the war, the holiday was abolished for various reasons. Still, many voices lamented its passing, so that in 1967 the day was again made a national holiday as National Foundation Day.