This is an ancient style of official communication, through which a high-ranking official expressed his gratitude or presented a petition to the emperor. Zhang, or memorial of gratitude, and biao, or memorial of petition, differed little in style. Liu Xie (465?-520) of the Southern Dynasties observed in his literary critique The Literary Mind and the Carving of Dragons that an ideal piece of writing should convey its essential message in a clear and in-depth way, state or analyze a case succinctly and thoroughly, and obey rules of ritual propriety and standards of writing.

It was officially decided at the beginning of the Qin Dynasty that a letter to the emperor should be renamed as a “memorial to the throne.” In the Han Dynasty, this form of writing was divided into four sub-types by the court: zhang, memorial of gratitude, zou, memorial of impeachment, biao, memorial of petition, and yi, memorial of dissent. (Liu Xie: The Literary Mind and the Carving of Dragons)

Memorials of gratitude or petition are intended to express gratitude to and extol the imperial court for the love and care it has shown to its subjects, or to present one’s true feelings. Such memorials should both demonstrate the authors’ literary talent and honor the empire. As these memorials are to be submitted to the court, they should be well-structured and eloquent in style. A memorial of gratitude or of petition should be explicit in wording. (Liu Xie: The Literary Mind and the Carving of Dragons)