Iranian Foreign Policy during the Sassanids
During the four centuries of the Sassanid rule, from the viewpoint of foreign relations, wars between Iran and Rome were the most significant events in the pages of history. In these wars there were several points worthy of attention, the foremost being the intervention of religion in the conduct of wars.
At the beginning of the 5th century A.D. under the leadership of a priest named Nestorius 42 a sect called Nestorians came into being among the Christians in the region of Syria. This sect differed from the other Christians in their beliefs, and for that reason they were condemned for heresy and excommunicated by the powerful church of that time in Constantinope, whereas the sect had a large following in the Middle East. Although Zoroastrianism was at that time the state religion of Iran, the government gave asylum to the Nestorians in order to gather a group of supporters between its own realm and Rome, its powerful neighbour. This support enabled the Nestorians to build churches in the realm of Iran and engage in propagating their religion.
The other point is that when the Roman Emperors saw that the powerful and centralised government in Iran had become a source of trouble for them, after revealing its intentions of conquering all of the Roman empire and moreover, owing to its distance from the territories of Iran and its inability to maintain watch over its distant frontiers, a powerful emperor of Rome named Constantine 43 decided to establish an eastern capital for himself. This coincided with the time when the Iranian emperor, too, had determined to establish a western capital at Tysphon in the territory of Iraq, while the Romans chose the city of Byzantine which later on became known as Constantinople. This change of capital from Rome to Constantinople produced many changes in the past history, the main factor of which was the vicinity of the two powerful neighbours who were engaged in constant dispute, not about any ideology, but about expanding their respective realms and conquering the world, namely personal motives.
Thus the foreign policy of Iran in this period was firstly dominated by religion, and secondly by the continued wars lasting four centuries. For one hundred years, there existed a peace pact between them, but for the rest of the period, namely for three centuries they were continuously in a state of war which became quite intense at the end of the sixth century A.D. That is in the time of Khosrow Parviz when intense wars raged between him and Heraclius, the Roman emperor. Both these emperors were contemporaries of the holy Prophet of Islam who sent written communications inviting them to embrace Islam. The war between the Emperors of Iran and Rome continued so long that they were losing their last ounce of strength. We will discuss these wars in more details later on when the subject of the birth of Islam comes up.
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42. Nestorious (380-451 A.D.) Bishop of Constantinople (428-431 A.D.), unlike the bishops of Alexandria who believed in the divinity of Jesus, believed that Jesus was the son of a human mother, and the unity of divinity and humanity in Jesus resembles the unity of a man and woman after marriage, namely two separate natures in a single body. He was exiled to the Lybian desert f or this belief and excommunicated.
43 Constantine the 1st (274-337 A.D.), vanquishing Maxence by the walls of Rome in 312 A.D. caused the recognition of Christianity as the official religion of the Rorhian emhhpire, transferred the capital to Byzantine which was given the name of Constantinople. This city was in 45 A.D. captured by Sultan Muhammad II of the Ottomans. Eastern Roman empire existed from 330 to 1461 A.D. - Dehkhoda Persian Dictionary. Vol. 5 and 6.
Adapted from the book: "Background of the Birth of Islam" by: "S. T. H. Khwarazmi"