A visitor to the city of Rome in the year 300 A.D. could traverse it without encountering one single building identifiable as Christian. It wasn’t that the Christian community wasn’t sizeable—indeed, the bishop of the city was already administering a large staff, distributing food to the poor, and communicating regularly through letters and emissaries with churches in other regions. But in Rome, as throughout the empire, churches were modest buildings, often in the style of domestic architecture, and could have easily been mistaken for private domiciles.

That was all about to change. A mere thirty years later, a visitor to Rome could not have missed the large buildings—such as the church on the site of the Lateran palace, dedicated to St. John—where newly public liturgies took place amid conspicuous splendor. Constantine’s benefactions to the Christian congregations in Rome paralleled larger gifts to those in Constantinople and in Jerusalem, where there were few Christians until Constantine established the city as a site commemorating the Resurrection, with a future as a pilgrimage destination and monastic homeland. His largesse legitimized Christianity’s public life while signaling its accumulation of riches and increasing exercise of power over the subjects and citizens of the empire. In this reading, Constantine’s victory over his rivals led to Christianity’s victory over Roman society and its conversion into a wealthy institution.

The eminent historian Peter Brown devotes the 700-plus pages of his absorbing new book to showing that this account is inadequate and untrue. In his telling, Christianity did not become the dominant religion thanks to Constantine; indeed, it did not gain vast property or become a distributor of largesse until more than sixty years later, during the reign of the emperor Theodosius. Certainly, Constantine legalized and enriched those Christian churches persecuted under his predecessor, Diocletian. But his aim, according to Brown, was never to establish the church as the sole religion of the empire. A Christian ruler, Constantine nonetheless repurposed a triumphal arch in Rome to celebrate his victories, much as his pagan predecessors had done; he did not prohibit the temples, but placed Christian ones beside them. In Brown’s view, the emergence of Christianity as an institution of wealth and distributor of charity began later, and took longer to develop, than is commonly believed—and Constantine could hardly have foreseen this development, let alone planned it.

Brown’s book covers two centuries in the life of Christianity and of the Roman Empire. His vast learning, accumulated over the course of nearly fifty years of published scholarship, helps flesh out this period so that readers can feel not just its ideas and preoccupations, but its shape and weight. Through the Eye of a Needle undertakes to demonstrate how, in the years from 350 to 550, the church in the West accomplished two great shifts. The first was the changeover from public benefactions to care of the poor, by which the wealthy now extended their munificence to the poverty-stricken, who depended on charity to fend off starvation. Previously, and following ancient Roman custom, the wealthy had arranged for displays of public-spirited distribution of wealth, and expected to be repaid by gratitude, loyalty, and commemoration on monuments. As Christians, they now poured their wealth into the church instead, to be directed to the church’s own ministries—ministries determined, in large part, by biblical injunctions to treat the poor with justice.

The second shift involved the collapse of Roman institutions that redistributed wealth. Before about 350, mediating wealth involved such practices as distributing imported grain to a hungry population. Now, the new institutions of the church—the strong metropolitan bishop and the monastic houses—were the repositories of wealth and the distributors of charity; they also became the first public hospitals. And as the central administration of the Roman Empire collapsed, this vacuum at the center all but forced regional churches and monasteries to form a network to replace Roman regional and civic organizations. Thus emerged the institutions upon which medieval Christianity was founded in Western Europe.

Through the Eye of a Needle takes Brown and his readers back to the world of his first book, Augustine of Hippo. In fact, we meet Augustine again, in his role as a preacher in fifth-century Africa. We meet other luminaries of his age as well, leaders of Christianity and architects of its wealth, whom Brown presents in a series of portraits. This book is long—like the amassing of wealth itself, it has taken time—and Brown divides it into five sections. Part One encompasses the period from the end of the third century to the end of the fourth. Brown shows that Christianity’s emergence into the public sphere did not begin with Constantine and the Edict of Milan. Christians were already present at the court of Diocletian; in fact, the Great Persecution was allegedly set off by the sacrilegious act of one of those Christians, crossing himself against a “demonic” god and arousing the fear and then the retribution of the emperors.

Apart from these persecutions, Christians and pagans mingled mostly peaceably in the world of the third century. (The era’s crises had other causes: unstable imperial rule, economic woes, and the press of the resurgent Persian Empire.) The tribal invasions of the north and west were still a century away, and these two groups, while different in worship and custom, shared much the same social profile—although there were few Christians among the senatorial class. Most, for now anyway, were of the middle class; only subsequently, during the fourth century, did they manage to move into the upper classes—by converting the fabulously wealthy—and to gain control of the government.

These achievements led to the redeployment of wealth away from civic monuments and, via the prophetic books of the newly authoritative Scriptures, toward charity for the poor. Brown writes that following “the absorption of the language and history of the Hebrew Scriptures in the Christian communities between the fourth and sixth centuries.... The poor were not simply others—creatures who trembled on the margins of society, asking to be saved by the wealthy. Like the poor of Israel, they were also brothers. They had the right to ‘cry out’ for justice in the face of oppressors along with all other members of the ‘people of God.’” Thus Brown records the turn of the wheel: the days of grandeur for its own sake had passed, and now grandeur was redeployed in churches whose orientation was toward the supernatural realm, guided by their Scriptures and traditions. The triumph of Christianity comes not thanks to Constantine, but rather to Theodosius, through whose Cunctos populos the Roman world was to become Christian, and Nicene Christian at that. And its duty, as John Chrysostom over in Antioch kept instructing his listeners, was to feed the poor.

The second section of Through the Eye of a Needle discusses this change through the lives of Symmachus, Ambrose, Augustine, Ausonius, Paulinus, Jerome, the clergy of Rome, and the wealthy Christian ascetic women who spread their largesse to particular leaders and to the churches as well. These biographies chronicle the personalizing of wealth management, disclosing that only through power, authority, and above all, rhetoric, did the church come to inherit the wealth of empire. The book’s third part, “An Age of Crisis,” surveys the fifth century and the breakup of the Western empire into regional kingdoms. Brown has traversed this territory before, in The Rise of Western Christendom, insisting against Gibbon that there was no decline and fall of an empire weakened by Christianity, but rather a transition to regional states that would in their way lay the groundwork for medieval Europe. Part Four, “Aftermaths,” takes the cases of Gaul and Italy to look at the successors to the empire; and Part Five, “Toward Another World,” looks at the sixth century and points to the little European kingdoms to come.

This book serves as a summation of, and key to, previous works of Peter Brown’s that together have formed both a field of inquiry—Late Antiquity—and a large cadre of disciples who now are scholars themselves. Brown has gone back over territory familiar to his readers of forty-plus years: the life of Augustine, the world of the later empire, the beginnings of Christianity in the West, the history that is neither material culture nor theology nor intellectual history, nor church history, but the history of a religious world in a structuralist sense. How, he asks, did it work? Brown reads the history cheerfully, with an eye for what was happening at the margins, where bishops and rulers of the future were constructing something new. Through the Eye of a Needle takes us back to a time when most Christians probably agreed, with Clement of Alexandria, that the division between rich and poor was permanent; a time when the class system of empire, like slavery, was taken for granted, and not every monk was poor. It is a book about wealth, and to possess it is to be the owner of a kind of wealth as well.