ENAn interest in the history of the borders of the Grand Duchy of Lithuania (GDL), on the one hand, and the Livonian branch of the Teutonic Order and the Duchy of Courland and Semigallia, on the other, arose in the 19th century historiography. The delimitation processes and the concept of borders have been and still are being researched. Sources relevant to these studies are published from time to time. In this case, a source found in the Latvian State History Archive is published: it is a border delimitation agreement concluded between the GDL and the Livonian branch of the Teutonic Order in 1541 to update the borders. The document is written in Latin, on parchment, and sealed. The treaty of 1541 similar in content was published back in the 18th century, but a closer analysis revealed that it is not the same document. The published document is an original that belonged to the Livonian side. A comparison of this text and the one published in the 18th century shows that they differ not only in the spelling of individual words, but also in whole fragments. This allows to take a new look at the documentation of the border delimitation processes. [From the publication]