The grouping together of Basil of Caesarea, with his friend, Gregory of Nazianzus, and his brother, Gregory of Nyssa, as the 'Cappadocian Fathers' is a product of modern scholars, who have regarded as significant the family links, geographical locality and common theological commitment they perceived in them. Theodosius was committed to Nicene orthodoxy and soon invited Gregory of Nazianzus to Constantinople, a largely Arian city, to be orthodox pastor in the Church of the Resurrection. He preached eloquently in defence of Nicene orthodoxy, his sermons there including the five theological orations to which he owes his title 'the Theologian'. The writings of Basil the Great can be divided into several categories: ascetic works, dogmatic works, homiletic works, letters, and a liturgy. Gregory of Nyssa seems to have been the Cappadocian for the twentieth century. There are a large number of dogmatic works, the most important of which is his Against Eunomius.

A striking difference between the porphyry portraits of the senior tetrarchs and the marble head of Constantine, the latter statue's clean-shaven face evokes portraits of Trajan, optimus princeps, and the first emperor, Augustus. The distinction between the porphyry and marble portraits points to another salient aspect of the fourth century, the alternation between periods of religious peace and conflict. Constantine's achievement of sole power as Christian emperor changed everything and nothing. His accession is, indeed, treated as a watershed by those who overlook the rapprochement between Christianity and Platonism in the late third century and who view Diocletian's persecution as the culmination of a sustained anti-Christian policy rather than an aberration. After Constantius' death, Julian moved quickly to put his own imprint on Roman power. Receiving reinforcements from Gratian, Theodosius' first task was to deal militarily with the Visigothic problem. In the East, Theodosius too became increasingly hostile toward traditional cult.

This chapter discusses the process by which the hints of the infinitely diverse religious climate that prevailed in much of the Roman empire in the fourth and fifth centuries have remained what they are for any modern reader - tantalizing fragments of a complex religious world, glimpsed through the chinks in a body of evidence which claims to tell a very different story. One tends to forget how much of the conflict between Constantine and Theodosius II, was considered by late Roman Christians to have been fought out in heaven rather than on earth. The late antique period is characterized by the successful imposition of a rabbinic interpretation of Judaism among the Jewish communities in Palestine, Mesopotamia and elsewhere, and by the formalization and propagation of Zoroastrianism throughout the Sasanian empire. Both are remarkable events of which we know singularly little, compared with the process that we call the 'Christianization of the Roman empire'.

At Thilsaphata Jovian met the forces of Procopius and Sebastdanus, which Julian had stationed in the area for the defence of Mesopotamia. The army was divided into two parts: the larger force accompanied Procopius to Tarsus with the body of Julian, and Jovian took the smaller to Antioch, diplomatically visiting the largest city of the eastern empire, where he hoped to make a better impression than Julian had done. Valentinian was an orthodox Nicene Christian. His tolerance in religious matters impressed pagans, many of whom had expected a violent response to Julian's michievous religious policy. In the spring of 368, Theodosius embarked his vanguard at Bononia and crossed the Channel to Rutupiae. An engagement between Theodosius and the Goths ended in a serious defeat for the Romans. After his accession Theodosius took time to understand fully the complexity of Greek Christianity.

The legacy of Theodosius I to the Roman world contained three elements of capital importance. First, his insistence that the Nicene version of Christian orthodoxy prevail routed Arianism from its strongholds in the Balkans and in Constantinople itself and laid down the lines of development for Roman Christianity, both east and west. Second, his settling as autonomous federates the barbarian peoples who had crossed into the Roman empire both before and after Adrianople, his gready increased use of federate troops in the Roman armies, and his cultivation of the chieftains of the barbarians, especially the Visigoths. Finally, Theodosius' determination that his dynasty should rule the whole Roman world led to a costly civil war against Eugenius and, at his own death shordy thereafter, the division of the empire between his two young and incapable sons, controlled by ministers whose rivalries split the resources of the state at a time when they needed to be united.

In the Roman tradition diplomacy, that is, 'direct communication state-to-state', was viewed mainly as an adjunct or epilogue to war, as when a victorious general negotiated the surrender of a defeated enemy, or an alliance was struck for a military goal, or a truce was agreed to forestall an attack or bury the dead. Information from the works, contextualized by the enormous amount of data now available from archaeology, makes it possible to construct a fairly ample account of the warfare of the period. The Greek and Latin sources begin to show a greater interest in diplomatic activity only during the later part of the reign of Theodosius II. Diocletian and Constantine completed the work of the third-century soldier-emperors in saving the Roman empire from its external enemies. The dangers latent in the federate settlements became clear soon after the death of Theodosius and the division of the empire between his ineffective sons, Arcadius and Honorius.