The present volume offers a new critical edition of an important treatise by Hilary of Poitiers (c. 315?–367/8), here given the title ‘Letter on the synods’ (‘Epistula de synodis’; manuscript titles vary and none can be considered ‘original’), accompanied by a helpful French translation of Hilary's sometimes challenging Latin. It is the first edition since that of the Maurist Pierre Coustant in 1693 (reprinted in PL x, 1845). The editor, Michael Durst, professor in patristics at Chur (Switzerland), is uniquely placed for this task; the treatise and its manuscript tradition were already the topic of his Habilitation in 1993 and have occupied him since. The full text of his earlier study has been made available online to accompany and supplement the discussion Durst offers in the introduction to the present volume (which lists manuscripts, offers a stemma and outlines the editorial principles on pp. 101–37). The treatise, written in exile, was addressed to Hilary's colleagues in Gaul (Durst holds that communion was not broken after his deposition in 356); a shorter second part looks towards eastern audiences. It principally traces the theological disputes in the east and make the case for the possibility of an ‘orthodox’ reading of the homoiusios-formula for western, pro-Nicene eyes as well as, in the concluding chapters, defending the term homousios against misunderstanding for eastern ears. Durst's meticulous discussion precisely dates the treatise to the winter of 358/359. The substantive introduction (pp. 9–137) discusses the historical and theological context in lucid detail, and analyses in particular the dossier of documents from the period that Hilary included to make his case. Important as the treatise is for understanding Hilary, the dossier of synodical texts he offers is arguably even more valuable for the understanding of the Trinitarian disputes in the 340–50s. Some of these exist in separate, independent traditions (and in Greek), for which their collection as Documents of the Arian controversy, edited by H. C. Brennecke and his collaborators (Athanasius Werke, iii, in several fascicles), must be compared. Durst has generously made available his text for the latter edition in advance. The present volume further includes the Apologetica responsa (‘réponses justificatives’), fifteen short passages that were written by Hilary himself as annotations to his treatise, from where they entered part of the manuscript tradition. They were addressed to Lucifer of Cagliari and answered his critical questions on specific points of Hilary's writing. Durst's edition here furnishes each annotation with a short, pertinent commentary; he dates the ‘responses’ to 360/361.

This masterful new edition of Hilary's De synodis is most welcome and will have to be used by every scholar interested in Hilary, his life and thought, and also by everyone concerned with the tumultuous theological disputes of the 350s. It is a significant achievement.