According to the 8th-century chronicles Nihon Shoki and Kojiki, Emperor Jimmu, descendant of the sun goddess Amaterasu, ascended the throne on this date in 660 BC, founding the Japanese imperial line. Modern Japan commemorates the date as National Foundation Day, a holiday revived in 1966 after being abolished following World War II for its association with State Shinto and imperial nationalism.
Emperor Jimmu almost certainly never existed as a historical figure; most scholars regard the first several legendary emperors in the Japanese chronicles as mythological constructs designed to root the imperial line in divine ancestry stretching back to Amaterasu, the sun goddess. The date itself, February 11, 660 BC, was calculated retroactively in the 19th century by Meiji-era scholars converting the lunar calendar reference into the Gregorian system, then adopted as 'Kigensetsu,' or Empire Day, in 1873.
The holiday became deeply entangled with militarist and ultranationalist ideology in the 1930s and early 1940s, celebrated with mass rallies affirming Japan's divine destiny. Occupying American authorities abolished it in 1948. It was reinstated by the Japanese government in 1966 under the more neutral name Kenkoku Kinen no Hi, National Foundation Day, sparking debate that continues today about honoring myth-as-history versus confronting the holiday's nationalist past.