The process of formation and cultural development of the Mordovians (the Mordva) in the Middle Ages is considered in the article. The Mordovian ethnos had started its formation process in the early Common Era by way of merger of small related ethnic groups. By the 8^th century, these groups united into two subethnoses – the Moksha and the Erzya, which have been preserved up to date. Four major stages are identified in the medieval history of the Mordva, which are mainly traced on the basis of archeological materials: 1) final stage of the tribal system (8^th–10^th cc.); 2) formation of the early Mordva states in the 11^th–13^th cc.; 3) the Mordva as part of the Golden Horde in the second half of the 13^th through to 15^th cc.; 4) the Mordva as part of the Russian State in the 16^th to18^th cc. For each period, the settlement area of the Mordovians, the characteristic features of their material culture, and the predominant directions of cultural relations are determined.