Between neighbours and rivals there were plenty of opportunities to learn about the political strategies and customs of the other. In this context, it must be emphasised that a transfer of technology and a curiosity with regard to the foreign culture can be observed in both directions. Scholarly literature often refers to a ‘difference in the degree of civilisation’ between West and East – this is not justified. The title of this chapter has therefore been chosen deliberately in order to stress an ‘exchange’ rather than a one-sided process. To give but one example: on many occasions the Sasanian Empire functioned as a mediator of cultural possessions from the Far East and India, which were eagerly received by the West.

The opportunity for exchange was not limited to the official political and administrative realms. It can be observed in particular with regard to the border regions (map 14), namely Mesopotamia and Armenia or border cities such as Dārā, Amida and Nisibis, where a frequent change of rule took place. ‘Enmity did not isolate the two empires from each other … A common language … and identical customs prevailed on either side of the frontier, linking together related populations split asunder by political accidents.’ In particular the geographic conditions in Armenia and Mesopotamia as well as to the west and south-west of the Euphrates, where the Syrian Desert formed the actual border between the great powers, prevented any strict control of this part of the frontier.

Roman monasticism in the early middle ages presents a paradox. ‘No other city in Christendom, save perhaps Constantinople, witnessed the flowering of monastic life as did Rome.’ The sources reveal a count of nearly a hundred monasteries founded in the City of Rome between the fifth and the tenth centuries. Forty-nine of these appear in the roll-call of Roman ecclesiastical institutions included in the Liber Pontificalis entry for Leo III in 806/7 – suggesting that eighth-century Rome, no less than Skellig Michael off the south-west coast of Ireland or S. Vincenzo al Volturno in the Abruzzi, played a part in the heroic era of monastic foundation in early medieval Europe. And yet, having enumerated the Roman monasteries of this period, there seems to be very little else we can say about them. Thus Guy Ferrari's (still indispensable) Early Roman Monasteries: Notes towards a History of Monastic Observance in Rome takes its title advisedly, as a warning to avoid disappointment on the part of those expecting a sustained analysis of the city's monastic life. The Notes are set out as a series of institutional biographies, in alphabetical order – but what Ferrari in fact shows is the impossibility of rendering the papal biographies of the Liber Pontificalis, and the evidence from other sundry documentary or epigraphic sources, into a coherent and satisfying fulfilment of his own scheme. In the fifty years since the publication of Early Roman Monasteries, no one has attempted to write up Ferrari's Notes.

In 2001 our Rom und das Perserreich. Zwei Weltmächte zwischen Konfrontation und Koexistenz was published by the Akademie Verlag, Berlin. Naturally, comments made by friends and colleagues as well as academic reviews encouraged us to think further about the issues of our book and also about its place among textbooks and scholarly works. We are hoping that Rome and Persia in Late Antiquity: Neighbours and Rivals, a revised and expanded translation, is an adequate response to the many suggestions we have received since 2001, among these the observation that our book did not have a counterpart in the English language that would correspond to its scope and format.

Even more than the German volume, the present study of Roman- Sasanian relations has been guided by our attempt to focus on the interests and independent policies of the eastern power. In reaction to the conventional and still prevalent eurocentric perspective of many scholarly works we emphasise the Eastern textual and visual testimonies. We have done so with the help of Ph. Huyse (Paris), who translated crucial passages from the trilingual Šāpāur Inscription (the Parthian text) as well as the inscriptions of the Zoroastrian priest Kartēr (Middle Persian) into English for us. Petra Sijpesteijn (Oxford) helped us with the translation of excerpts from Arabic texts and David Taylor (Oxford) with the Syriac texts. Thank you!

We have expanded our study by including a new chapter on the role of Armenia (26). Here, we are grateful to Tim Greenwood (St Andrew's), who not only translated the Armenian passages but also gave patient advice on the interpretation of the material. Moreover, the new book has chapters on Sasanian warfare (II.2) and on the relationship between rulers (II.8).

Historians of late Roman Christianity, especially those of a Gibbonian stripe, take delight from this extraordinary account of the no-holds-barred contest for the papacy in 366, and the resulting massacre in the Liberian basilica of the supporters of Ursinus. But they rarely take heed of their source. The text stands at the opening of the Collectio Avellana, a mid-sixth-century collection of nearly 250 documents relating to the bishopric of Rome in the fourth, fifth, and sixth centuries. While its account of Damasus is frequently cited, the Collectio as a whole is something of a backwater, in both medieval and modern scholarship. This obscurity is surely undeserved, and it obtains only because we have asked the wrong question. As an early medieval canon law collection the Collectio is indeed a virtual dead end – far less successful and important than the near-contemporary collection of Dionysius Exiguus.

Relations between Romans and Persians in late antiquity were bound to be turbulent, to say the least. We are looking at those who conquered the possessions of the heirs of Alexander the Great versus those who claimed to be the heirs of the Achaemenid Empire, which was conquered by Alexander the Great. ‘Heritage’ and its claims often foreshadow war, in this case centuries of warfare that lasted throughout the existence of the relationship between the two powers, i.e. the third to the seventh century ad. On both sides war was accompanied by complex attempts to justify their respective goals, in both active and reactive ways. Rome's claim for world domination was accompanied by a sense of mission and pride in Western civilisation; it was met by Eastern myths and oracles prophesying the downfall of the Western power. Our sources reflect strong Roman ambitions to become a guarantor of peace and order. Simultaneously, they reflect long-standing prejudices with regard to the Eastern power's different customs, religious structures, languages and forms of government. As a consequence, a wide gap separated the two cultures and negative attitudes that stemmed from existing political, military and economic rivalries were constantly reinforced. In the company of most ancient – and often Western – observers, it is tempting to associate our theme with an ‘everlasting’ conflict between West and East, between a ‘civilised’ Roman world and a barbarian enemy, and hence to describe the struggle between the two super powers as a clash of fundamentally alien cultures.

This approach is a phenomenon that applies not only to antiquity but also to the present day, possibly more than ever before.

On the Monte Celio, the transformation of Rome from late ancient to medieval city appears to unfold before our eyes. A short walk from the Colosseum takes one to the Clivus Scauri, an exquisitely preserved Roman street running up the hill, and to the formidable redoubt of Christian monuments built around it. To one side, the monastery of S. Gregorio, founded by Gregory the Great on his own property, and its satellite chapels. Immediately adjacent is the so-called ‘bibliotheca Agapeti’, a reminder of the Christian university planned by Pope Agapetus. Behind this cluster, on the eastern slope of the hill, is the Lateran Palace, commissioned by the emperor Constantine in the fourth century, and the regular residence of popes from the seventh. Archaeologists are now persuaded that Constantine's palatial development was accompanied by interest in the neighbourhood from the most powerful private investors in the city, the Anicians. By 400, the dynasty was well established there, having converted shops and houses into a massive residential complex – the direct or indirect parent of the papal stronghold that took shape in the sixth century.

The shift from private mansion to ecclesiastical redoubt seems still more powerfully enacted on the other side of the Clivus Scauri, in the church of SS. Giovanni e Paolo. According to their passio, John and Paul were executed in the reign of Julian the Apostate (361–363), and buried in their house; under the sponsorship of a senator Byzantius and his son Pammachius, the house became a church.

Writing in 413 to Anicia Juliana, the mother of the recently dedicated virgin Demetrias, Augustine of Hippo expressed his concern that her daughter had been preyed upon by the author of a dangerous letter containing novel doctrines on divine grace. The letter to which Augustine referred was indeed dangerous: it was none other than the now famous Epistula ad Demetriam of Pelagius, the manifesto in which the holy man made known to influential members of the Roman church the ideas on the nature of the soul for which he would eventually be condemned as a heretic. Augustine's implication is that despite or perhaps because of her exalted social standing, Demetrias was in danger of becoming a pawn in a high-stakes game of ecclesiastical authority. Augustine knew – as Pelagius would have known – that by addressing the letter to a figure so exalted as Demetrias, its contents would acquire an aura of respectability for a wider readership that would be difficult, if not impossible, to dispel. The letter is one of the few undisputed works of Pelagius to survive.

This feuding among regions and cities in central italy was now incidental to imperial concerns, because increasingly central Italy itself had become peripheral. So had the city of Rome. At the end of the third century a Gallic orator described a map of the Roman world that was being painted on the wall of a new school at Autun. This map highlighted the regions where the four emperors who made up the Tetrarchy had enjoyed recent military successes. Those regions included Egypt, where Diocletian had suppressed a rebellion; Africa, where Maximian had defeated the Moors; Batavia and Britain, where Constantius had overthrown a usurper; and the eastern frontier, where Galerius had triumphed over the Persians. The orator did not mention Rome. If the map had provided a caption for Italy and Rome, then the absence of an emperor and his court would have been all the more glaring. The emperors now resided and campaigned in the frontier zones that enclosed the Roman world and rarely visited the provinces around the Mediterranean center.

THE OUTER RIM

This map still noted the activities of emperors in Africa and Egypt. Soon emperors no longer visited those regions either. Constantine's reign confirmed the shift in political significance from the western and southern regions of the empire to the eastern and, especially, the northern regions. Centuries earlier, Roman armies had first expanded outside Italy in campaigns against the rival empire of Carthage in North Africa.

Constantine replied to the petition from hispellum and the other Umbrian cities sometime after late December 333, and most likely before mid-September 335. During this period he was either in or near Constantinople, or he was campaigning in the Balkans. Unless there had been a long delay in his response, the cities had presumably sent their petition shortly before.

ITALY FOREVER

Hispellum and these other cities in Umbria were reacting in part to fairly recent changes in the administration of Italy. Already during Augustus' reign the peninsula had been divided into eleven geographical regiones. The region that included Rome was, of course, the first region, and through his patronage and favoritism Augustus made clear that no other city in the empire, in particular one of the great cities in the East such as Alexandria or Antioch, would become a rival: “hereafter Rome would never be anywhere but in Rome.” In central Italy north of Rome the upper Tiber River divided Etruria (sometimes known as Tuscia) as the seventh region from Umbria to its east as the sixth region. Since central and southern Italy shared in the elevated prestige of Rome, from the beginning the cities of peninsular Italy had long had a favored standing within the empire. “Italy tended to be treated by the emperors as something of an extension of the city of Rome.” Augustus and his successors funded municipal buildings, temples, walls, and aqueducts, provided aid after natural disasters, and built or repaired roads everywhere.

In our postmodern times irony rules, and every reading of the past is presumed to have some validity. To argue their interpretations historians resort to various techniques, including the selection, highlighting, and rearranging of texts and artifacts. By those criteria the passage of time can qualify as an interpreter of history, since it too has shuffled the stuff of the past into unexpected configurations. The passage of time is not just the subject of history; it has also, in its own mysterious way, provided “readings” and interpretations of the past. Nor are these memories to be dismissed as haphazard, and therefore meaningless for the historical enterprise. In fact, in some respects the passage of time has provided readings that are truly thought provoking in their unpredictable playfulness. While many modern historical narratives are burdened by their own theoretical jargon and ponderous seriousness, the passage of time seems to have a mischievous sense of humor.

The fate of the inscription at Hispellum is one example of the playfulness of time. The people of Hispellum had wanted their own imperial temple and festival. After Constantine's favorable response they constructed their temple, appointed their priests, celebrated their festival, and renamed their city. They also erected a permanent record of the emperor's rescript on a large stone slab over five feet high and almost two feet wide.