The article examines different opinions of the XVIII - XX centuries historians concerning controversial evidence of the sources on the time of the first buttle between the Russians and the Mongolians on the Kalka-river. Historiographical analysis allows to find out that a commonly accepted version of the dating of the battle (may 31, 1223) lacks reliable grounds as it was based on the information of foreign sources whose authors had no idea of the exact time of the battle. This research results in the conclusion that only thorough study of chronological testimony of russian annals can help to solve the problem definitely.