Ruthenian language
In the 13th–18th centuries, Belarusians were known as "Ruthenians" and spoke Ruthenian language, while being part of the Grand Duchy of Lithuania, which conquered the lands of White Ruthenia, Black Ruthenia, and Polesia. Casimir's Code of 1468 and all three editions of Statutes of Lithuania (1529, 1566, and 1588) were written in the Ruthenian language. From the 1630s it was replaced by Polish, as a result of the Polish high culture acquiring increasing prestige in the Polish–Lithuanian Commonwealth.