The main aim of this article is to research the information linked with Mongolian invasion to the Galician–Hungarian borders area and to establish the date of the crossing by the Mongols of the Russian Hungarian border. The authors have come to several conclusions. Firstly, both Russian annals and Persian annals do not contain the information that could set a timeline when the Mongolian army crossed the Russian-Hungarians borders. Secondly, to set the correct timeline of the Mongolian invasion to Hungary, the basis for the research the main source can be “The Sad Song for the Destruction of the Kingdom of Hungary by the Tartars” by Rogerius of Apulia who was the witness of the Mongolian invasion to Hungary and was captured by the Mongols. Thirdly, the main reference point to set the timeline of the events related to the Mongolian expansion was the dating of the period of the Great Fast in 1241 which made it possible to check the dating of the events related to the destruction of the Hungarian kingdom. Fourthly, the authors managed to date the beginning of the Mongols’ offensive to the Hungarian border, which was not previously used in the historical science because the use was made of the date of the battle at the Veretsky mountain pass.DOI 10.14258/izvasu(2017)5-30