The first years of Justinian were marked by missionary fervor, to destroy all remnants of heresy or paganism, and to use every means available to create compliance with orthodoxy. Christianity was also to be spread beyond the boundaries of the empire. Religion was a motivating factor in several foreign policy initiatives of the late 520s, which began in 526, the last year of Justin's reign. There is little doubt that Justinian, who now shared power with his uncle, was responsible for this aggressive policy. The hostilities with the Sassanians in the Caucasus region in 526 were prompted by religious differences. There were three kingdoms aligned south of the Caucasus between the Black Sea and the Caspian; Lazica in the West, Iberia in the center, and Albania in the East. When Kavad, the Persian king, tried to impose fire worship on the Iberians, their Christian ruler Gougenes appealed to Justin to protect the region. Despite long-standing Persian influence among the Lazi, their ruler Ztathius, dressed in a mixed Roman-Persian garb, was converted to Christianity, baptized, and officially crowned by Justin.92 The crucial details about Ztathius' conversion are an indication of Roman motives.
The Romans also extended their grip in the Colchian region by subduing the highland people of Tzani, who “changed their way of life to a more civilized one, enlisted in Roman levies, and ever since have joined the Roman army against its enemies. They also changed their beliefs for a more pious way of life, all of them having become Christians” (Procopius, Bell. Pers. 1.15.25; see p. 370). In 527 Malalas tells us that Gord, the king of the Huns living near the Crimean Bosporus, also came to Justin in Constantinople and was baptized. Returning to his people he attempted to impose Christianity on them, meeting furious resistance from the Huns' pagan priests. Justin then followed up his initiative by sending a fleet manned by Gothic soldiers to impose peace on the Bosporan area (Malalas 18, 432–3). From the moment that hostilities with the Persians had been resumed in 526, it was Roman policy to turn the Black Sea into a Christian lake.
Religion and trade are the keys to understanding Roman intervention at the southern extremity of the eastern frontier, around the Arabian Sea. The Romans supported the Christian ruler of the Ethiopian Axumites in a successful war against their neighbors in the Yemen, the Himyarites (Homeritai). According to Malalas, the latter, who followed a form of Judaism, had been interfering with Christian traders traveling through the Yemen from the East to do business with the Axumites. Their king Dimnos now sent an embassy to Alexandria, offering his subservience to the Roman Empire and asking that a bishop and clergy be sent them to baptize his people.93 Procopius has a much fuller and more detailed account of these events, explaining the circumstances under which the Axumite Ethiopians imposed a new Christian ruler on the Himyarites. Justinian's role was to send an ambassador, Julianus, to require the two nations, on account of their both being Christian, to join together as allies against the Persians. Procopius indicates that one of the Romans' important objectives was to establish the Ethiopians as the key middle-men in the silk trade between India and Constantinople, thereby intercepting the profits which the Persians were making from this (Procopius, Bell. Pers. 1.20). The religious motives of the Romans appear from another detail. Justinian also ordered the demolition of the pagan sanctuaries at Philae in the upper Nile valley, which had been maintained up until Procopius' own times (Procopius, Bell. Pers. 1.19.36–7).
Justinian had adopted a more aggressive stance against Persia from the moment that he became sole ruler. His first order was given to Belisarius, the commander in Mesopotamia, to build a new frontier fortification at Mindouos, even closer to Nisibis than Dara was (Procopius, Bell. Pers. 1.13–14). The Sassanian attempt to prevent the fortification of Mindouos gave Justinian a casus belli, and he appointed Belisarius to full command of the troops of the diocese of Oriens, with instructions to make for Nisibis. The main front was in Mesopotamia, the traditional cockpit of warfare between the two empires (Map 4.3). Control of Nisibis since 363 gave the Persians an enormously important forward position, which reduced the strain of moving troops long distances through hostile territory before they could make significant incursions against the Romans. Dara had been built as a bulwark against invasion along this route, and was the crucial position at the center of the Roman defense system. A large scale battle was fought outside the walls of Dara in 529. The Persians were defeated, but obdurately held their ground diplomatically, demanding that the Romans continue to pay the traditional subsidy to pay for the defense of the Caucasus passes against the Huns, and that they demolish their illegal forts at Dara and especially at Mindouos (Procopius, Bell. Pers. 1.16).
Map 4.3 The Roman–Sassanian frontier in the sixth century
A Saracen raid, led by the Lakhmid leader Alamundaras (al-Mundhir), exposed Syria's weak defenses and almost reached the walls of Antioch in 529 (Malalas 18, 445). In 531 a combined force of Sassanians and Saracens, avoiding the heavily fortified and garrisoned cities of Mesopotamia, crossed the middle Euphrates near Callinicum, and headed again for Antioch. Roman troops forced them to retreat but suffered serious losses in a battle on the Euphrates, although the Persian force was unable to deliver a decisive blow.94Belisarius was recalled to Constantinople and the eastern command transferred to Mundus.
In September 531 the long-lived Sassanian king Kavad died, to be succeeded by Khusro (Chosroes) I. Khusro himself was faced by internal rebellion. Meanwhile, in January 532, Justinian's own attention was entirely focused on events at Constantinople, the catastrophic week-long Nika riot in Constantinople, which ended with 30,000 dead. These events helped to persuade both sides to agree to end a war that neither could win. The Romans returned fortresses which they had occupied in Persarmenia, while the Persians gave up their claims to control Lazica. The Iberians were allowed the choice of remaining in exile in Lazica under Roman rule, or returning to their homeland under Persian protectorate. The Romans abandoned Mindouos, but maintained the fortifications and their garrison at Dara. They also agreed to pay an indemnity of 11,000 pounds of gold as their contribution to the cost of the Caucasus garrison (Procopius, Bell. Pers. 1.22).
Such were the basic terms of the so-called Endless Peace. The outcome was highly satisfactory from the Roman point of view. All the major gains that had been made between 526 and 529, especially around the Black Sea, had been retained and consolidated. The Mesopotamian bulwark around Dara had held firm, and the cities of northern Mesopotamia and Syria had been spared serious damage. Moreover, the Persian threat was blunted by the Sassanian regime's internal fragility (Procopius, Bell. Pers. 1.23).