Increasingly, students of late antique Christianity and early Islam are coming to understand their two areas of research as organic parts of one broader historical whole. Our current condition can be likened to one in which – to borrow an image borrowed by Thomas Sizgorich for other purposes – two English neighbours are having a cordial conversation from either side of a fence. As Sizgorich points out, a growing number of multi-author publications embrace studies of Christianity and Islam between the same covers. What Thomas Sizgorich aspires to offer is a synthesis illustrating how the Islamic communities under formation from the seventh to the ninth centuries should be understood along a spectrum of late antique religious communities, rather than as ‘somehow discrete from the world in which [they] took shape’ (pp. 147–8).

With Violence and belief, Sizgorich has taken a step forward by writing approachably about the fourth to ninth centuries, wearing lightly the specialist's knowledge of Greek, Syriac and Arabic sources in a way which will not alienate readers more comfortable on either the Classical or Orientalist side of the fence. We still await the finely-hewn historical synthesis, but what we have to thank Sizgorich for is a stimulating addition to the on-going debate on how to talk about Christian–Muslim relations in language other than ‘borrowing’, ‘debt’ and such terms which no longer satisfy our desire to understand the intricately interconnected communities which flourished in this period. Instead of owing debts and borrowing, we find Christians and Muslims ‘reformulating’, ‘elaborating’, ‘evolving’, as well as ‘imbibing’ and even occasionally ‘being influenced’. The helpful paradigm Sizgorich encourages us to consider is that of ‘a koinê of signs, symbols, and narrative forms with which the other [i.e. pre-Islamic] communities of late antiquity had for centuries contested questions of divine revelation, prophetic legitimacy, communal integrity and eruptions of the numinous into the lived experience of individuals and communities’ (p. 13).

Sizgorich is especially concerned with the way in which communities describe and circumscribe themselves with words: his first chapters offer examples of self-definition through the construction of narratives, meta-narratives and emplotment. The once physically conceived mare nostrum becomes a semiotic pool from which different late antique communities draw. Particularly helpful among the many theories of community identity is Geertz's notion of cultural DNA, by which we may discern ‘certain family ‘affinities’' between different late antique community narratives (pp. 165, 278–9). The narrative that most interests Sizgorich promotes self-definition of the aggressive sort: he argues that

Paradoxically, in a book replete with gory details, the fundamental problem is its lack of flesh and blood. Too often abstractions are given verbs, as if that is enough to breath life into them. Do we really ‘perform’ identity? And the problem of transmission from this common gene pool of codes and symbols is never properly addressed. One longs for examples of how the shared narratives moved from individual to individual and not just from text to text. We learn a lot about literary topoi but not enough about historical context and development.

Much of the first two-thirds of the book is occupied with bellicose line-drawers, but Sizgorich does not forget those whose taste was for more peaceful co-existence. In a rather unflagged shift, Sizgorich turns toward the end of the book, particularly in the last chapter and conclusion, to less violent attempts to navigate what he aptly calls the ‘messy world’ of ninth-century religious polyphony. Throughout the book, Sizgorich's method is to select a few ‘high profile’ individuals – John Chrysostom, Ambrose, Libanius, Ibn al-Mubārak – and examine how they or their neighbours delineated their communities from those around them, often through violent means, by constant adaptations to a shared late antique language. His final example is the great jurist Ibn Ḥanbal, who stands apart from the others for his inward shift in the definition of jihād. It is as if in the end Sizgorich does not have the stomach for all the religiously-justified violence he carefully details, and he might better have entitled his book Varieties of intolerance and tolerance in the late antique east. We learn a lot about both, especially through his use of later Arabic sources such as Abū Nu'aym al-Isfahānī (d. ad 1038/ah 430), relating vignettes of individual and communal accommodation of and resistance to the Other. Some developmental analysis of the sources used would have alerted the reader to the hazards of retrojection, especially since the book is intended to reach scholars beyond those specialising in early Islamic history.

The presence throughout Violence and belief of a subtle longing for co-existence made this reader at least wish that the author had taken a deep breath, put the book aside and reconceived it. Had Sizgorich been more of an ascetic warrior against himself, he would not have been lured by the siren-call of tolerance and diversity, but instead he would have focused exclusively on how communities used violence to maintain their boundaries: his chapter on Libanius' Pro templis and his analysis of militant monks and early mujāhidūn are both enlightening. But Sizgorich is too curious an historian, and he gets drawn to other texts, though he does not, puzzlingly but perhaps as a good infidel, touch the Qur'ān – there are also more technical flaws: the repetition of several quotations which saps their punch and the frequent misuse of the word ‘numinous’, as in ‘numinous military conquest’ (p. 257). At this point life gets more complicated and we see that monks were not only monomaniacal fighters in the eyes of early Muslims. Monks and monasteries provided a vast and varied array of raw material for developing new narratives, and Sizgorich allows himself to dip briefly into that more aesthetic, less ascetic dimension of the shared late antique world of monkery (pp. 238–9, 268–70). But now the horizon opens onto burgeoning eighth- and ninth-century genres of Arabic literature about monasteries and wine, inspired partly by monastic culture, from which Sizgorich wisely restrains himself, although he could perhaps have suggested further reading for others less reserved. As it is, such understandable curiosity militates against his original devotion to violence – a mortal danger against which the Khajirites constantly warned. The result is a somewhat indecisive, messier book, whose tendency to include rather than exclude, however, more closely reflects the behaviour of the majority of people in the period Sizgorich studies.