This publication is the first publication in Russian historical science of the work of the envoy of the papal curia, Master Rogerius, who was in Mongol captivity, “A Song of Sorrow about the Ruin of the Hungarian Kingdom by the Tatars.” Contains important and sometimes unique information on the history of the Kingdom of Hungary, neighboring countries and peoples, as well as the Mongol invasion of Central Europe in 1241-1242. Mentions the actions of the Russian contingents of the Mongol army. A number of Latin-language documents from 1241-1248 are published in the Appendices to this edition. (mainly letters and acts), illustrating certain nuances of Master Rogerius’s narrative.