_Sassanian Period._--In 226 the Parthian empire gave place to the new kingdom of the Sassanidae, whose claim to the ancient Achaemenian empire led to constant struggle with Rome in which Edessa naturally suffered. The native state was restored by Gordian in 242; but in 244 it became again directly subject to Rome. The Edessan martyrs Sharbel and Barsamya, whose "Acts" in legendary form have come down to us, may have perished in the Decian persecution. In 260 the city was besieged by the Persians under Shapur I., and Valerian was defeated and made prisoner by its gates. Odaenathus of Palmyra (d. 267), however, wrested Mesopotamia from the Persians; but Aurelian defeated his successor Zenobia at Emesa (273), and Carus, who died in 283 in an expedition against the Persians, and Galerius (297) carried the frontier again to the Tigris. Diocletian's persecution secured the martyr's crown for the Edessenes Shamona, Guria (297), and Habbib (309), and shortly thereafter Lucian "the martyr," who though born at Samosata received his training at Edessa; but the bishop Qona, who laid the foundations of "the great church" by the sacred pool, somehow escaped. Edessa can claim no share in "the Persian Sage" Aphrahat or Afrahat (Aphraates); but Ephraem, after bewailing in Nisibis the sufferings of the great Persian war under Constantius and Julian, when Jovian in 363 ceded most of Mesopotamia to Shapur II., the persecutor of the Christians, settled in Edessa, which as the seat of his famous school (called "the Persian") grew greatly in importance, and attracted scholars from all directions. He taught and wrote vigorously against the Arians and other heretics, and although just after his death (373) the emperor Valens banished the orthodox from Edessa, they returned on the emperor's death in 378. Under Zenobius, disciple of Ephraem, studied the voluminous writer, Isaac of Antioch (d. circ. 460). Rabbula perhaps owed his elevation to the see of Edessa (411-435), in the year which produced the oldest dated Syriac MS., to his asceticism, and it was to his time that the sojourn there of the "Man of God" (Alexis) was assigned; but he won from the Nestorians the title of the Tyrant of Edessa. In particular he exerted himself to stamp out the use of the Diatessaron in favour of the four Gospels, the Syriac version of which probably now took the form known as the Peshitta. When the popular Nestorianism of the Syrians was condemned at Ephesus (431) it began to gravitate eastwards, Nisibis becoming its eventual headquarters; but Edessa and the western Syrians refused to bow to the Council of Chalcedon (451) when it condemned Monophysitism. In and around Edessa the theological strife raged hotly.[21] When, however, Zeno's edict (489) ordered the closing of the school of the Persians at Edessa, East and West drifted apart more and more; the ecclesiastical writer Narsai, "the Harp of the Holy Spirit," fled to Nisibis about 489.