It is to be lamented, that Bayer has only given a Dissertation de Russorum prima Expeditione Constantinopolitana, (Comment. Academ. Petropol. tom. vi. p. 265 - 391.) After disentangling some chronological intricacies, he fixes it in the years 864 or 865, a date which might have smoothed some doubts and difficulties in the beginning of M. Leveque's history.