One of the first Russian historical and ethnographic study of the Mordovian people (Mordvins) in the context of Russian-Mordvinic ties and cultural relationships, undertaken by the famous writer M. (literary pseudonym Andrey Pechersky). The essays were published in 1867 in the popular research magazine ‘Russky vestnik’ and became the basis for analyses of the Volga-Finnish ethnic component in the narration about the ‘uprising of Magi’ in the Primary Chronicle. Despite the fact that the authr himself did not consider his work as a specialized scholarly research, and the ‘Essays…’ were not completed by him, the general scale of the coverage of material made the text more significant than anything published on the Mordvinic topics earlier. The search for common features in the culture of the Mordvins and Russians, the Christianization of the Mordvins, the formation of the Church structure in their land, as well as the fixation of the syncretic nature of the Mordvinic cosmogonic and anthropogonic myths were the main thread of the ‘Essays…’. A whole chapter was devoted to the description of Mordvinic collective prayers with sacrifices and their classification. Completing his study, M.-P. came to a controversial but innovative for his time conclusion about the identity of the pre-Christian beliefs of the Mordvins and those of Eastern Slavs.