to codify reading pronunciations and the associated rhyme conventions of regulated verse. The Qieyun (601) was an attempt to merge the distinctions in six earlier dictionaries, which were eclipsed by its success and are no longer extant. It was accepted as the standard reading pronunciation during the Tang dynasty, and went through several revisions and expansions over the following centuries.

The Qieyun is thus the oldest surviving rhyme dictionary and the main source