East
For many non-Russian ethnic groups both within and outside contemporary Russia, it is a common second language and {{link=lingua franca">lingua franca . Since the Middle Ages, Russian has gradually expanded its speech area from its historical locus in the upper Volga and Dnieper River drainages northward and eastward. Russian speakers penetrated Siberia in the 16th century and reached the Pacific in the 17th century. Russian became a full-fledged literary language in the 18th century, when it finally displaced Church Slavonic (see Old Church Slavonic language ). Dialect differences in Russian are not great, considering the enormous territory over which it is spoken, and the upheavals of the 20th century eroded such distinctions as exist.