of the emperor; he completed it, submitting 30 volumes of history and one volume of genealogy". References The Nihon Shoki is a synthesis of older documents, specifically on the records that had been continuously kept in the Yamato court since the sixth century. It also includes documents and folklore submitted by clans serving the court. Prior to Nihon Shoki, there were Tennōki and Kokki compiled by Prince Shōtoku and Soga no Umako, but as they were stored in Soga's residence, they were burned at the time of the Isshi Incident. The work's contributors refer to various sources which do not exist today. Among those sources, three Baekje documents (Kudara-ki, etc.) are cited mainly for the purpose of recording diplomatic affairs. Textual criticism shows that scholars fleeing the destruction of the Baekje to Yamato wrote these histories and the authors of the Nihon Shoki heavily relied upon those sources. This must be taken into account in relation to statements referring to old historic rivalries between the ancient Korean kingdoms of Silla, Goguryeo, and Baekje. Some other sources are cited anonymously as aru fumi ("; other document), in order to keep alternative records for specific incidents. Exaggeration of reign lengths Most scholars agree that the purported founding date of Japan (660 BCE) and the earliest emperors of Japan are legendary or mythical. This does not necessarily imply that the persons referred to did not exist, merely that there is insufficient material available for further verification and study. Dates in the Nihon Shoki before the late 7th century were likely recorded using the Genka calendar system. For those monarchs, and also for the Emperors Ōjin and Nintoku, the lengths of reign are likely to have been exaggerated in order to make the origins of the imperial family sufficiently ancient to satisfy numerological expectations. It is widely believed that the epoch of 660 BCE was chosen because it is a "xīn-yǒu" year in the sexagenary cycle, which according to Taoist beliefs was an appropriate year for a revolution to take place. As Taoist theory also groups together 21 sexagenary cycles into one unit of time, it is assumed that the compilers of Nihon Shoki assigned the year 601 (a "xīn-yǒu" year in which Prince Shotoku's reformation took place) as a "modern revolution" year, and consequently recorded 660 BCE, 1260 years prior to that year, as the founding epoch. Kesshi Hachidai For the eight emperors