Under the Hàn, the Chinese language undergoes several transformations. This is why Hàn period Chinese is considered as a transitional language between Old Chinese (see previous posts) and Middle Chinese.
Under the Western Hàn (221-207 BC), Literary Chinese (wényán 文言) is consolidated, both in how it is written (characters), and in what is written (syntax, vocabulary). The great texts of the Warring States period are edited and annotated.
The work that epitomises this period of the Chinese language is the Records of the Grand Historian (Shǐjì 史記) by famous historian Sīmǎ Qiān (司馬遷).
Under the Eastern Hàn (9-23 AD), Literary Chinese is used to translate Buddhist scripture into Chinese. It is the first time that written Chinese is confronted to foreign written languages, and this process enriches the literary Chinese language.
It is also under the Eastern Hàn that spoken Chinese (vernacular Chinese) and written Chinese (wényán) start to diverge significantly. Texts written in Late Old Chinese are not readily understood any longer. They are annotated and partially translated into Hàn period Chinese. Wényán remains the written language used by the administration and by writers of "serious" texts. Its role is comparable to the one played by Latin in Europe. Although it is constantly influenced by vernacular Chinese and enriched by neologisms and loanwords, wényán becomes a dead language by the 3rd century AD.