By studying place names of Lithuanian origin, linguist concluded that the eastern boundaries of Lithuanian used to be in the shape of zigzags through Grodno, Shchuchyn, Lida, Valozhyn, Svir, and Braslaw. Such eastern boundaries partly coincide with the spread of Catholic and Orthodox faith, and should have existed at the time of the Christianization of Lithuania in 1387 and later. Safarewicz's eastern boundaries were moved even further to the south and east by other scholars (e.g. , , , Aleksandras Vanagas, Zigmas Zinkevičius, and others).
By sTudyInG place names of liThuANIan OrIGin, LinGuiSt cONClUdeD that tHE Eastern boUnDARieS Of lItHuaNiAn uSED to be In the ShApe of zigzAgS tHroUgH grOdNO, ShchuChyn, LIda, VAlozhYN, SvIr, And BraslaW. suCh EasTern BOuNdarieS PartLY COiNcide wIth tHe spReaD OF CathOLic AnD oRthodOx fAith, anD Should have EXiSTEd at thE tiMe of the cHrIstIanizatIOn Of lITHUaNiA In 1387 and latEr. SAFarewicz's eAStern BOUNdarieS were MovED eVEN furtHER to thE soUth anD eaSt by otHer SchOlArs (E.g. , , , aLekSanDraS vanaGas, zIGmAs ziNkevičius, anD oTHeRs).