"Tongdian", one of the "ten links". The first political treatise with complete style in the history of China was written by Du You, a politician and historian in the Tang Dynasty, which specifically discussed the evolution and changes of laws and regulations in past dynasties. The book consists of 200 volumes, including diet, election, official position, ceremony, music, military affairs, criminal law, prefectures and counties, frontier defense, etc., with more than 500 subheadings1900,000 words. Tongdian records the evolution of laws and regulations from topaz era to the end of Tianbao in Xuanzong of Tang Dynasty, especially in Tang Dynasty.
Tongdian occupies an important position in the history of historiography and is the pioneering work of the history of special laws and regulations. The history of Du You's previous laws and regulations is basically concentrated on the book records in biographical history books. Limited by historical facts and narrative style, it is impossible to undertake the task of completely recording the development and change history of social, political and economic systems. Tongdian (five volumes in total) separated this genre and opened up a broad world for its development. Since then, the history of canon system has become an important category in traditional historiography.