The Huanglan or Imperial Mirror was one of the oldest Chinese encyclopedias or leishu "classified dictionary". Cao Pi, the first emperor of the Wei, ordered its compilation upon his accession to the throne in 220 and it was completed in 222. The purpose of the Huanglan was to provide the emperor and ministers of state with conveniently arranged summaries of all that was known at the time. Complete versions of the Huanglan existed until the Song dynasty (960-1279), when it became a mostly lost work, although some fragments did survive in other encyclopedias and anthologies. The Huanglan was the prototype of the classified encyclopedia and served as a model for later ones such as the (624) Tang Yiwen Leiju and the (1408) Ming Yongle dadian.