Sasanian Empire and the Roman-Byzantine Empire were recognized as the two leading world powers, for a period of more than 400 years. Frequent Persian aggression during the 3rd century placed Roman defences under severe strain, but the Romans were eventually successful in warding these off and avoiding any territorial losses. Indeed, they eventually made significant gains towards the end of the century, although these were reversed in the mid-4th century. By that time conflicts attained an added religious dimension. It is in this context that the future of Roman–Persian relations would be played out over the remaining centuries, continuing into the Byzantine era. Neither side was able to inflict a decisive and convincing military victory against the other, and the movement between hostilities and diplomacy would continue to play out between each power. According to some sources, two years before his death, Shapur I married a daughter of Aurelian, and attempted to further Romanize the city of Gundeshapur, which was mainly populated by the Roman prisoners-of-war back then. In the 5th century, Romans provided a subsidy as the Sassanians requested, to construct defenses in Derbent, through which incursions from tribes of the northern steppes endangered both empires. In 395 AD, 18,000 Roman populations of Sophene, Armenia, Mesopotamia, Syria, and Cappadocia were captured and deported by the "Huns". the prisoners were freed by the Persians as they reached Persia, and were settled in Slōk (Wēh Ardashīr) and Kōkbā (Kōkhē). The author of the text Liber Calipharum has praised the king Yazdegerd I (399–420) for his treatment of the deportees, who also allowed some to return. See also Italy–Iran relations Parthia Romans in Persia Roman Empire Byzantine Empire Roman–Persian Wars Roman–Parthian Wars Sassanid dynasty Acacius of Amida Mithraic mysteries Notes References K. Butcher, Roman Syria and the Near East, Getty Publications, Los Angeles, 2003 R. C. Brockley, East Roman Foreign Policy, Francis Cairns Publications, Leeds, 1992 Further reading Full historical overview of Byzantine-Iranian relations Foreign relations of Iran Parthia Ancient international relations