Recent books on Constantine have been numerous and span the spectrum from popular works to very specialised monographs. One thing they generally have in common is their focus on existing controversies, even when they apply new methodologies. S. treats a rather less well-mined area, Constantine's relations with Shapur and the Persian Christians, focusing on Constantine's Letter to Shapur that was embedded in Eusebius' Life of Constantine. While, as a result, this work may not find a wider audience, S. offers a compelling argument for reconsidering the history of this contested frontier.

S. analyses Constantine's Letter to Shapur, which he suggests was written in 324–25 (p. 20), and concludes that the text was not only non-threatening, but deliberately distanced Rome from Valerian the persecutor of Christians, and further points out that Constantine's tone in the letter was treated as irenic by Sozomen. S. goes on to argue that Shapur was not, in fact, persecuting Christians, reasoning that Ammianus and Julian, neither of whom were friendly to Christianity, treated the war not as a crusade, but as any other border struggle. S. does not press the point as firmly as I believe he could, but an item worthy of note is Julian's invasion of Persia, where he was following Constantine's invasion plan but certainly not with the intention of rescuing Christians (cf. W.E. Kaegi, ‘Constantine's and Julian's Strategies of Strategic Surprise against the Persians', Athenaeum 59 [1981], 209–13). Indeed, the persecution of Persian Christians seemed to have escaped the eastern sources themselves, as Christians with knowledge of local traditions such as Ephrem and the author of the Syriac Julian Romance present Shapur without mention of his persecution, with the Julian Romance going as far as to show Shapur as a ‘peacemaker’. Ultimately, S. concludes ‘There was no controversy or cover-up: Constantine was not going to war for Christians when he died’ (p. 64). Although S. dismisses those who have argued that the letter was a cause for war (T.D. Barnes, ‘Constantine and the Christians of Persia’, JRS 75 [1985], 136), as well as those who have argued that a lacuna in Eusebius deliberately suppressed a failed invasion of Persia (G. Fowden, ‘The Last Days of Constantine’, JRS 84 [1994], 148; R. Burgess, ‘ΑΧΥΡΩΝ or ΠΡΟΑΣΤΕΙΟΝ: the Location and Circumstances of Constantine's Death’, JTS 50 [1999], 156, 161), it must be said that he manages to do so irenically, although, like that of Constantine, his tone may be misconstrued.

It is a secondary matter, but I believe S. missteps when he writes of the mid-350s as a time of ‘conflict’ between Julian and Constantius II (p. 71), as this was well before Julian's acclamation as Augustus in 360 and is contradicted by evidence indicating a functional working relationship between the two in their campaign in Gaul at that time (G. Bowersock, Julian the Apostate [1978], pp. 38–9; E.D. Hunt, ‘The Successors of Constantine’, in CAH XIII, p. 29). The volume is generally well-edited, but does occasionally misspell names (‘Han Drijvers’, p. 90) or drop a preposition (‘According Ammianus’, p. 73).

There is more to S.’s monograph, with further material on later authors and three translated texts in the appendices providing a jumping-off point for further research. The work is supported by a current bibliography and an index that thankfully includes modern authors. Those treating fourth-century Roman–Persian relations or the history of the Eastern church will now have to engage with S.’s well-developed argument.