See Emperor Justinian’s letter from 560 and the response of the Armenian bishop Gregory Arzeruni about the date of Christmas and the celebration of the Annunciation: Michael van Esbroeck, “La lettre de l’empereur Justinien sur l’Annonciation et la Noël en 561,” Analecta Bollandiana 86 (1968), pp. 351–371; Michael van Esbroeck, “Encore la lettre de Justinien. Sa date: 560 et non 561,” Analecta Bollandiana 87 (1969), pp. 442–444; Lorenzo Perrone, La Chiesa di Palestina e le controversie Cristologiche. Testi e ricerche di scienze religiose 18 (Brescia: Paideia, 1980), pp. 127–139.