Nihongi Ryaku (日本紀略)
Nihongi Ryaku (Summary of Japanese Chronologies) is a Japanese history text compiled during the Heian period which contains excerpts from Rikkokushi (the Six National Histories) and details of the history from the completion of Rikkokushi until the reign of Emperor Goichijo. The content covers the history from the age of the gods to the year 1036. It is not known who compiled the text. It is organized in chronological order, written in Kanbun (classical Chinese) style and contained within 34 volumes.
Nihongi Ryaku is said to have been created between the latter half of the 11th century and the 12th century but the exact time is unknown. It is also not known who compiled the text. The original name of the text is unclear. It is also known as "Nihon Shigiryaku," "Nihon Shiryaku," and "Nihon Shirui."
It appears as though the opening text pertaining to the age of the gods was not originally contained within the text but was incorporated after completion.
The first half of volume 20 covering the period until the reign of Emperor Koko is an abridged version of the main section of Rikkokushi. However, it is not an exact copy as the wording was revised in order to shorten its length.
There are also sections in which new text not found in Rikkokushi has been added. The section pertaining to the assassination of FUJIWARA no Tanetsugu and the exile of Imperial Prince Sawara contains valuable text which was deleted from "Shoku Nihongi" (Chronicle of Japan Continued) for political reasons. "Nihongi Ryaku" is also helpful in better understanding the sections lost from "Nihonkoki" (Later Chronicle of Japan).
Descriptions of period from the reign of Emperor Uda to Emperor Goichijo between 887 and 1036 are not excerpts but were created by the compiler of "Nihongi Ryaku." It appears as though "Nihongi Ryaku" referred to "Shinkokushi" (New National History) for the source of material, but the daily records contained within are not accurate.