the plains of northern vietnam were under chinese control for most of the period from 111 bc to ad 938 and, after independence, the country adopted literary chinese as the language of administration and scholarship. as a result, there are several layers of chinese loanwords in vietnamese. the oldest loans, roughly 400 words dating from the eastern han, have been fully assimilated and are treated as native vietnamese words. sino-vietnamese proper dates to the early tang dynasty, when the spread of chinese rhyme dictionaries and other literature resulted in the wholesale importation of the chinese lexicon.