Old Russian language
The Old Russian language, also called the Old Ruthenian language was a language of the ancient Rus'. It should not be confused with the Church Slavonic, Old Church Slavonic nor the Russian languages. This Old Russian language is the predecessor to the the modern Ukrainian, Rusyn, and Belarusian languages. Together with the Old Church Slavonic language, it also contributes to the modern Russian language.The Tale of Igor's Campaign is one of the few surviving literary works in this language.
Obviously, it is difficult to assess this language as a kind of a language norm in the modern sense. With limited literacy, the spoken language in Rus' consisted of a variety of dialects, and today we may speak definitely only of the languages of surviving manuscripts. Since, at these times, manuscripts were written in monasteries, a significant influence of Old Church Slavonic was inevitable.