Vasily Tatishchev believed that for the first time the term "White Rus'" is found in the Rostov chronicles in the year 1135, where the lands of Rostov-Suzdal Principality were mentioned.
[2] The praiseworthy songs composed in the second half of the 14th century by the Austrian poet Peter Suchenwirt tell how in 1349, in the battle of Izborsk ("Eysenburk" in the poem), German knights faced "Weizzen Reuzzen" ("White Russians").
[5]An ethno-religious theory suggests that the name used to describe the part of old Ruthenian lands within the Grand Duchy of Lithuania that had been populated mostly by Slavs who had been Christianized early, as opposed to Black Ruthenia, which was predominantly inhabited by pagan Balts.
[6] As stated by historian Andrej Kotljarchuk, the first person who called himself "Belarusian" was Calvinist writer Salomon Rysinski (Solomo Pantherus Leucorussus, ca 1569-1626).
According to his words, he was born "in richly endowed with forests and animals Ruthenia near the border to frigid Muscovy" and doctorated at the University of Altdorf.
[citation needed] Also, the 16th century chronicler Alexander Guagnini's book Sarmatiae Europeae descriptio wrote that Rus' was divided in three parts.