In this impressive, well-documented monograph the author explores the effect of legal practice, especially argument in court, on the Roman law of late antiquity, notably the law of heresy and the emerging canon law of the Christian Churches. The book comes in three parts. In the first the author explores the role of forensic practitioners (judges, legal experts and advocates, the first and last of which were often not legally trained) in the development of late Roman law. In the second she focuses on those forensic practitioners who used their expertise to further the interests of the late antique Church either in relation to the courts and civil law or in regard to early canon law. The final part deals with the distinction between orthodoxy and heresy, particularly in relation to the courts. Humfress makes good use of ecclesiastical writers and theologians as well as of the more obvious legal and literary sources.

In Humfress's view not only was there, as a number of authors have argued, more continuity between pre-Christian law and the law of the later empire, as seen by lawyers and the imperial bureaucracy, than used to be supposed but the practice of forensic advocacy continued much as before. It was embraced by many educated Christians. Indeed the cognitio system of procedure ‘actually increased the opportunities for advocates and iurisperiti to influence the development of the law on a case-by-case basis through their activities in court’ (p. 28). In the later empire the rhetorically trained were not restricted to literary ambitions. Forensic advocacy offered them a potentially lucrative career that required a training over several years and, like law, equally time-consuming in this respect, provided the competent with a prospect of upward social mobility. Rhetorically trained practitioners were able through arguments in court or in informal dispute settlement, suggestions for legislation, advice to bishops, membership of imperial bureaus, or serving as judges, to influence the ongoing development of the law through its interpretation and application in practice. This was particularly true of the vacillating distinction, continually renegotiated from Constantine onwards, between orthodoxy and heresy. Neither designation came ready-labelled and both needed to be constructed. Several of the eastern and western advocates listed in two valuable appendices (pp. 273–91) were Christians and were able directly or indirectly to influence the construction of the distinction between orthodoxy and heresy. Its construction was reflected in and reflected imperial constitutions, the decisions of church councils and ecclesiastical writings, but was shaped also by arguments about how opinions aimed at courts, officials or religious opponents, should be designated. Was Nestorius a ‘Simonian?’ Was Priscillian a ‘Manichee’?: ‘The ability to make a theological name stick like mud became an important tool in the prosecution of heresy cases under the later Empire’ (p. 241).

Why was heresy socially important? From a legal point of view accusations of heresy were, then as now, usually motivated by the desire of the accuser to legitimate a claim to power (for example, of the Emperor Maximus) or to establish a claim to own or possess property (pp. 243–68). References in constitutions to Manichees, Priscillianists or Donatists, even if phrased in wide terms or given a general scope by being embodied in the Theodosian Code or Justinian's Corpus Iuris, are often prompted by claims to church or family property. Indeed the author argues that, quite apart from heresy, much imperial law-making was occasioned by the impact of particular disputes, ‘driven by concrete cases rather than abstract principles or rules’ (p. 61). This is surely correct, and the earlier phenomenon of the very numerous case studies (disputationes, responsa, rescripta) in which the texts of legal authors treated real or hypothetical instances of litigation continued in altered form into the later empire.

Inevitably, given the book's novel and somewhat radical thesis, a reviewer has some reservations. Some faulty translations are incautiously copied. ‘In melius produci’ (p. 63) means ‘improved’ not ‘clarified’. The emphasis on rhetorically trained advocates sometimes leads the author, in my view, to treat a lawyer (iurisperitus in her terminology) as a rhetorician or to exaggerate the legal expertise that could be acquired by attending a school of rhetoric or by arguing cases in court. A case in point is Tertullian, the theologian writer, whom she declines (pp. 173–5) to identify with the legal author some of whose texts are included in Justinian's Digest, since his works display not only legal but rhetorical skills. But Libanius' view that legal training damages rhetorical expertise is self serving. It should not be taken at face value. Most lawyers had received a rhetorical education before they went on to the specialised (as it were post-graduate) discipline of law. Not all of them then adopted the plainer style and more restrained mode of argument that marked many of the leading legal authors. Court decisions did not necessarily make precedents. As the history of English law demonstrates, decisions in particular cases generate law only when collected and made available for use in later cases. In the ancient world this required a codex or at least a document that could be consulted readily. Decisions, even if enforced or enforceable, did not automatically make law.

These are minor quibbles. Humfress's engaging book makes an original, incisive contribution to our understanding of the continuity of legal practice in the later empire and to the role of forensic advocacy by Christians in the genesis and elaboration of the distinctions between orthodoxy and heresy that evolved in the post-Constantinian world. Unfortunately these distinctions were too often formalised as state law. The gradual fusing of civil law and Christian traditions did not either in the ancient world or later create overall a single system of law; and it would have been better if issues of theological orthodoxy had not been sporadically incorporated into a system that was genuinely civil in that it concerned relations between people rather than relations between them and the divinity.