[1][2] Several authentic sources, surviving from the Middle Ages, with expressed opinion of the Grand Dukes of Lithuania themselves prove that the Lithuanians (founders, rulers of Lithuania from the Gediminids dynasty) were those who spoke Old Lithuanian and originated from the cultural regions of Aukštaitija and Žemaitija, while their Eastern neighbours were Rus' people (Ruthenians): "We do not know on whose merits or guilt such a decision was made, or with what we have offended Your Lordship so much that Your Lordship has deservedly been directed against us, creating hardship for us everywhere.
First of all, you made and announced a decision about the land of Samogitia, which is our inheritance and our homeland from the legal succession of the ancestors and elders.
That peace was made in the one thousand three hundred and thirty-eighth year of the birth of God, on All Saints' Day, with the consent of the Master, the Marshal of the Land and many other nobles, as well as the City Council of Riga; they kissed the cross on the matter; With the consent of the King of Lithuania [ Gediminas ], his sons and all his nobles; they also performed their sacred rites in this matter [ Pagan rites ]; and with the consent of the Bishop of Polotsk [ Gregory ], the Duke of Polotsk [ Narimantas ] and the city, the Duke of Vitebsk [ Algirdas ] and the city of Vitebsk; they all, in approval of the said peace treaty, kissed the cross."
[9] The poet-monk Klymentiy Zinoviyiv [uk] who published several cultural studies noted that Litvins, perhaps after an older pagan tradition, worked on Sundays and rested on Fridays.
[9][11] The name Litvin (Litvyak) owes its origin to political factors and is a demonym (politonym) referencing the Grand Duchy of Lithuania.
[14] Some Belarusians like Mikola Yermalovich and Viktor Veras (Виктор Верас) claim that the Grand Duchy was Belarusian and that modern Lithuanians are "historical Samogitians" (the term Samogitia translates as Lowlands of Lithuania proper) who, despite being "not Lithuanians", somehow managed to usurp the name "Lithuania" for themselves.
[22][23] The Grand Duchy of Lithuania is called Велике князівство Литовське (Velyke kniazivstvo Lytovske).