Anastasius of Sinai, writing c. 700, told the story of a doctor who saw, at the shrine of St Epiphanius, many sick people who hoped for healing. He observed that, with God's help, several could be treated by conventional medicine; and with the archbishop's permission, he cured them.

In the last half century, most scholarship on late antiquity has accepted the irresistible rise of the cult of saints, but Matthew Dal Santo explores the scepticism and resistance which was answered explicitly in treatises and implicitly in saints’ Lives. Do souls survive the death of the body? If they survive, are they asleep until the resurrection? If they are asleep, how can saints heal or appear in visions or make intercession? If they are awake, how, without the body, can a soul perceive or be perceived? (Disembodied survival remains a philosophical problem: see Richard Sorabji, Self [Oxford 2006], 304–15.) Can saints themselves do miracles, or is it always God who acts, perhaps through angels who take the appearance of saints? Is it idolatrous to venerate saints? And if we are judged on what we do in the body (2 Corinthians v.10), how can the dead benefit from the Church's prayers and offerings?

These questions were not new in the late sixth century, but Dal Santo finds social and intellectual reasons for new urgency. Rulers were more eager to claim that saints supported their rule; churches were more eager to provide ritual care for the dead; people at risk from invasions and epidemics doubted that saints could protect them. More people read Aristotle (see now Josef Lössl and John Watt [eds], Interpreting the Bible and Aristotle in late antiquity, Farnham–Burlington, Vt 2011), who challenged confidence in the immortal separable soul and reinforced demands for rational and empirical proof rather than citations of authorities; Stephen Gobar, according to Photius, set out opinions of the Fathers in pairs of contradictory statements. Dal Santo's fascinating material sets Gregory in a context of debate ranging from the fourth to the eighth centuries, from Rome through Constantinople and the eastern Mediterranean to Baghdad, in Latin and Greek and Syriac. Gregory himself served as papal ambassador in Constantinople, and debates, like trade, crossed boundaries of language and government.

Gregory's Dialogues on the miracles of the Italian Fathers (written 593/4) are of special importance for western tradition because they include the Life of St Benedict and discussion of purgatory. Dal Santo argues (chs i–ii) that they are not simple hagiographic tales for the uneducated, but address concerns also found in Eustratius On the state of souls after death (written at Constantinople in the late sixth century), in other treatises, and implicitly in saints’ Lives. Eustratius and Gregory used biblical and patristic authorities to argue that souls are active after death. Divine and human energies interact in the miracles and appearances of saints, which are evidence for the afterlife of the soul, just as in life the invisible soul is inferred from its activity. Some earlier writers accepted that saints go directly to heaven; Eustratius and Gregory thought it followed that sinners go directly to hell, so there is an individual judgement after death. What then happens at the Last Judgement? The bliss or anguish of the resurrected body is added to that of the soul; for those between saint and sinner there is purgatorial fire, but the mass can help them.

In Dal Santo's reading, other saints’ Lives (chapter iii) implicitly answer doubts. It was indeed Cosmas and Damian, Cyrus and John, who healed the sick, and Demetrius who saved Thessalonica; the disputed miracles of Symeon the Younger really were miracles. Theodore of Sykeon was so near death that the angels came down from heaven, but near him was an icon of Cosmas and Damian, who asked the angels to wait while they successfully interceded for more years: saints, then, are independent of angels, and their disembodied souls look like their icons. John the Almsgiver interceded after his death for a woman who had asked for his help.

Chapter iv explores the different tradition of the East Syrian Church, where the cult of saints coexisted with belief in ‘soul sleep’ until the resurrection of the body. Ephrem held that the soul after death is conscious only of itself until it is reunited with the body. Before that, even the penitent thief cannot be with Jesus in Paradise, and the souls of the saints rest in Eden; the benefit of prayer and intercession is deferred until after the resurrection. Narsai of Nisibis, probably influenced by tradition rather than by Aristotle, affirmed the union of body and soul, which meant that the soul is dormant without its instrument, and cannot be saved or damned on its own. Ishai emphasised that we, not the saints, benefit from commemorating them. In East Syrian hagiography, Dal Santo finds little on post mortem appearances, miracles and intercessions, and incubation at shrines. By 790, at Baghdad, a bishop who was suspected of heresy had to include soul sleep in his statement of orthodoxy; but the Catholicos Timothy i was still asked the familiar questions.

This book is a development of a doctoral thesis. Occasional typos, and some small errors in translations, have escaped the copy editor, and the appendix on Anastasius and Ps.-Athanasius could have been integrated into the text. But these are minor concerns. The book connects Gregory to a wider Byzantine world which was not united in its reverence for saints and sacramental priesthood. Dal Santo shows how large-scale theories of social and religious change bring more texts into focus, and how detailed study of those texts modifies the theories.