The reign of Khusro I (531-579) was a key-period for the history of the Sasanian Empire. Nevertheless, sporadic persecutions of Christians converted from Zoroastrianism are attested. Among these martyrs, there were famous people of civil society such as Grigor Piran-Gusnasp, general-in-chief of the king's armies, Yazd-panah, a high dignitary and judge, and 'Awira, a courtier. The most famous was the Catholicos Mar Abba (540-552), who reunified the Church of the East after nearly twenty-five years of schism; canonist and exegete, he also restored ecclesiastical discipline which had been significantly weakened since 484. He is known to have been involved in Mazdeo-Christian controversies and polemical debates with West-Syrian Christians. These narratives written by contemporaries to the events are the only East-Syrian hagiographies of that time in Syriac; they provide valuable informations regarding socio-religious and political situation of the sixth century Orient. A critical edition based on manuscripts from the London, Berlin and Vatican Libraries, including a translation in French with a commentary, is presented for the first time.