Book of Song
Over 20 histories of the Jin had been written during the Northern and Southern dynasties, of which 18 were still extant at the beginning of the Tang dynasty. Yet Emperor Taizong deemed them all to be deficient and ordered the compilation of a new standard history for the period, as part of a wider 6-history project to fill in the gaps between the Records of the Three Kingdoms, the Book of Song, the Book of Qi, the Book of Wei and the Emperor's own time. As part of this ambition its treatises cover not only the Jin but also the preceding Three Kingdoms, making up for the lack of such a section in the Records of the Three Kingdoms.