Nihon kōki

is an ancient history of Japan written in 843.
This work is the third of the "Rikkokushi" ("Six National Histories"). It was written after the "Nihon Shoki" and the "Shoku Nihongi".
Fujiwara no Otsugu, Fujiwara no Yoshino, Fujiwara no Yoshifusa, Minamoto no Tokiwa, Asa no Katori and Yamada no Furutsugu were the main editors. 
"Nihon Kōki" is a primary historical source of information about Japan's Nara period and Heian period. 
The work covers the 135-year period from the beginning of Emperor Mommu's reign in 697 until the 9th year of Emperor Juna's reign in 832. The text is an account of twelve imperial reigns.