In using documents of this kind for purposes of historical investigation, as for instance in order to determine the day on which a historical personage died, the appeal must always be to the local sources. In the case of saints belonging to the Western Church no importance must be attached to the fact that the Easterns may have transferred them to a different day, and _vice versâ_, as, for example, in the case of St Ignatius of Antioch. Where the day is given in some local source, otherwise deserving of credit, we can be then certain that it is correct. This must be done with regard to SS. Peter and Paul, for whom the local sources give invariably the 29th June, while foreign calendars give other dates, as we find is the case with Polemius, Silvius, and the Arian martyrology. The compilers of these calendars wished to celebrate the Princes of the Apostles, but, being ignorant of the actual day of their death, placed them on any day that seemed suitable. Finally, at a later date the correct date came to the knowledge of foreign churches, and found its way into their calendars. 9. _The Kalendarium Marmoreum of Naples_ In the ninth century, a time of great activity in matters relating to hagiography, the Church of Naples undertook a revision of its calendar, which exhibits noteworthy peculiarities. First of all, nearly every day of the year is provided with the name of a saint, which indicates considerable care and study. This result was achieved by following the Eastern custom of admitting Old Testament personages, although not to the same extent. The grounds on which the selection was made cannot be discovered, for we have Abraham on the 9th October, Isaac on the 17th March, Eliseus on the 28th November, Daniel on the 17th December, Zacharias on the 13th May, while other important personages, such as Isaias, etc., are omitted. We are also reminded of eastern usage by the commemoration of the council of Ephesus on the 4th August, and other traces of eastern influence are noticeable in the admission of a few bishops of Constantinople, such as Metrophanes, and also of the names of Constantine (without Helena) on the 21st May, and Theodosius on the 10th November. With regard to Metrophanes, the compiler is guilty of a remarkable oversight; he has placed him once on the right day (the 4th June), without his title, and again on the 4th January with his title, “_Patr. Const._” The confusion between the 4th of June and the 4th of January might easily escape a transcriber, and must have already existed in the source which the compiler used. In order not to omit any name the compiler preferred to enter the same name twice, once with, and once without, its proper title.