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1.1.1. The exact dates of the deaths of Abba Isaias and Peter the Iberian and the dates of Peter’s memory
The traditionally accepted date of the death of Peter the Iberian is December 1, 491. The date December (First Kanon) 1 is stated explicitly in the Life of Peter the Iberian, and the year 491 follows from chronological evaluations made by scholars. However, both Life of Peter the Iberian and Syrian calendars give somewhat contradictory information. This fact was recently noticed but never explained by Cornelia Horn.
The chronology of the death and the burial of Peter the Iberian according to his Life is the following:
· Abba Isaias died on August (Ab) 11, year is not specified (§ 167),
· memory day of John the Eunuch, October (First Teshrin) 4, passed (§ 171),
· vision of an Egyptian monk Athanasius who lived with Peter as his disciple, that took place ten days before the death of Peter: bishop-martyr Peter of Alexandria will arrive for the soul of Peter the Iberian; the memory day of Peter of Alexandria was to take place in seven days (§ 173),
· liturgical service of Peter on the memory day of Peter of Alexandria (§ 175),
· an account on some “blessed Stephen” who died after Peter the Iberian; his memory day is First Kanon (December) 4, “three days after the memorial of Abba Peter, our bishop” (§ 177),
· another vision of the same Athanasius, a priest-monk from Egypt: the death of Peter the Iberian will occur on that same day which is the third day of the feast of Peter of Alexandria, “according to the custom that one adopted in Alexandria, that his memorial was [to be celebrated] for three days” (§ 180),
· Peter the Iberian died on that same day (§ 181),
· “It was then late evening, [near] dawn on Friday”; the body of the saint was wrapped and prepared to the burial (§ 182),
· Peter’s burial in his monastery in Maiuma at the evening of the second day after his death (§§ 186–188),
· Peter’s relics translation to the new monastery building “during the following year, one day before [the anniversary] of his departure” (§ 191),
· a kind of summary of the chronological data in the final chapter of the Life: Peter died on First Kanon (December) 1, “when Sunday was dawning” [cf. Friday in § 182 above], on the third day of the memorial of Peter of Alexandria, five months after the departure of Abba Isaias [cf. August as the month of Isaias’ departure in § 167 above: from August to December there are only four months], the translatio of his relics took place in the second year, one day before Peter’s memorial; Peter’s first deposition took place on First Kanon (December) 2; thus, we celebrate Peter’s memory during three days: the day of his translatio, the day of his death, and the day of his first deposition (§ 193). Horn already noticed that “[t]his description conflicts with the dating of the commemoration of the Peter of Alexandria indicated above at Vit. Pet. §182” but one can see some other contradictions as well.
Despite its unawareness of the exact date of the death of Abba Isaias, the last chapter of the Life of Peter the Iberian is quite precise in its justification of the memory cycle of Peter constructed around December 1 as its main date. Indeed, we can see this date as that of the memory of Peter in some Syrian calendars. December 1 fell on Sunday in 491. This seems to me being the main argument for dating of deaths of both Peter the Iberian and Abba Isaias to 491. However, it is difficult to avoid an impression that the whole final chapter of the presently accessible text of the Life of Peter the Iberian is a later addition. In fact, it does not have any support in the bulk of the text. The note in § 177 that the memory of blessed Stephen on December 4 is “three days after the memorial of Abba Peter” could be also a later gloss, if it contradicts to the other relevant data.
According to the main text of the Life, Peter’s death took place on November 27, the third day of the feast of Peter of Alexandria which started on November 25. Indeed, this date is also known to Syrian calendars. November 27 fell on Friday in 492. It seems to me, thus, beyond any reasonable doubt that the exact dates of Abba Isaias’ and Peter the Iberian’s departures are August 11, 492, and November 27, 492, respectively.
As it is stated in the Life of Peter the Iberian (§ 180), his death took place within a liturgical cycle of Egyptian origin, the three-day feast of Peter of Alexandria. According to the Egyptian calendar, the date of Peter the Iberian’s death is Koiak 1. This fact is the obvious source of confusion in a part of the Syrian liturgical tradition. In the Middle Ages as well as in the Antiquity, it was rather customary to “translate” the dates from one calendar to another without any exact formulas but simply on the ground of identification of the months which are roughly corresponding to each other. Thus, Egyptian Koiak is to be interpreted as Julian December (First Kanon, in Syriac), and Koiak 1 becomes December 1 instead of November 27. The final chapter of the presently accessible text of the Life of Peter the Iberian is an elaborated attempt to justify an already established liturgical cycle based on such mistake. This chapter is a later addition with no historical value.
 In her analysis, Horn interprets the dates according to the Alexandrian (Coptic) calendar without discerning properly between the Julian calendar and the Gregorian one. Thus, she rightly states that the memory date of Peter of Alexandria is November 25 (Julian calendar) but, then, translates the same date, Hator 29 (= Julian November 25), as December 8 (Gregorian calendar from March 1900 till February 2100), which produces a series of chronological confusions in Horn’s commentaries. Cf. Horn, Phenix Jr, John Rufus…, 263, n. 6, and 264, n. 2.
 Horn, Phenix Jr, John Rufus…, 242/243. The Life of Abba Isaias by Zacharias gives no chronology at all; cf. E. W. Brooks, Vita Isaiae monachi auctore Zacharia Scholastico, in: Vitae virorum apud monophysitas celeberrimorum, I (Parisiis, 1907) (CSCO, Ser. III, Syr 25 [7–8, Syr 7–8]) 1–16 (txt) / 1–10 (versio).
 Horn, Phenix Jr, John Rufus…, 248/249.
 Horn, Phenix Jr, John Rufus…, 252/253–254/255.
 Horn, Phenix Jr, John Rufus…, 256/257.
 Horn, Phenix Jr, John Rufus…, 258/259.
 Horn, Phenix Jr, John Rufus…, 262/263.
 Horn, Phenix Jr, John Rufus…, 262/263–264/265.
 Horn, Phenix Jr, John Rufus…, 264/265–266/267; Horn’s note (p. 264, n. 2; see above) that it is December 10 is wrong, unless we adopt the Gregorian calendar when its difference with the Julian one is 13 days.
 Horn, Phenix Jr, John Rufus…, 270/271–274/275.
 Horn, Phenix Jr, John Rufus…, 278/279.
 This contradiction was noticed by R. Raabe, Petrus der Iberer. Ein Charakterbild aus Kirchen- und Sittengeschichte des fünften Jahrhunderts. Syrische Übersetzung einer um das Jahr 500 verfassten griechischen Biographie. Herausgegeben und überstetzt (Leipzig, 1895) 132, n. 2.
 Horn, Phenix Jr, John Rufus…, 278/279–280/281.
 Horn, Phenix Jr, John Rufus…, 279, n. 6.
 Calendar Nau VI; Nau, Un martyrologe et douze ménologes…, 67. The calendar of Rabban Sliba gives Peter’s memory two times, on December 1 and on November 25 (instead of the memory of Peter of Alexandria that is to be expected on this day); P. Peeters, Le martyrologe de Rabban Sliba, Analecta Bollandiana 27 (1908) 129–200, here 142, 143/168, 169 (txt/tr.).
 Calendars Nau III; Nau, Un martyrologe et douze ménologes…, 48, and Nau X; ibid., 108.