The name Rus’ is often conflated with its Latin forms Russia and Ruthenia, thus Belarus is often referred to as White Russia or White Ruthenia. The name first appeared in German and Latin medieval literature; the chronicles of Jan of Czarnków mention the imprisonment of Lithuanian grand duke Jogaila and his mother at “Albae Russiae, Poloczk dicto” in 1381. In some languages, including German and Dutch, the country is generally called “White Russia” to this day (Weißrussland and Wit-Rusland respectively).
The Latin term “Alba Russia” was used again by Pope Pius VI to recognize the Society of Jesus there 1783, exclaiming “Approbo Societatem Jesu in Alba Russia degentem, approbo, approbo.” The first known use of White Russia to refer to Belarus was in the late-16th century by Englishman Sir Jerome Horsey, who was known for his close contacts with the Russian Royal Court. During the 17th century, the Russian Tsars used “White Rus” to describe the lands added from the Grand Duchy of Lithuania.
The term Belorussia (Russian: Белору́ссия; the latter part similar but spelled and stressed differently from Росси́я, Russia) first rose in the days of the Russian Empire, and the Russian Tsar was usually styled “the Tsar of All the Russias”, as Russia or the Russian Empire was formed by three parts of Russia—the Great, Little, and White. This asserted that the territories are all Russian and all the peoples are also Russian; in the case of the Belarusians, they were variants of the Russian people.