The story of the forged Constitutum Constantini is one of the most fascinating, and indeed notorious, of medieval history. The document tells, in words purporting to emanate from the emperor Constantine himself, the history of Constantine's conversion and baptism at the hands of pope Sylvester; and how, in return, Constantine conferred a vast array of authorities and privileges on the papacy, most especially authority – in some form – over the western provinces. This done, the emperor departed to Constantinople in the east, not deeming it proper for imperial power to operate in a sphere now under more spiritual authority.

Unsurprisingly, given its contents, this document played an important role in medieval debates regarding the powers of the papacy and the relationship between theological and political spheres, Church and Empire. Its value and impact, however, were not constant: it was something of a double-edged sword, since the very idea that papal powers derived from an emperor rather than a more directly divine source was not without difficulties; the nature of the powers conferred was hotly debated; and even the basic validity of papal claims based on it was at times challenged, well before Lorenzo Valla's famous exposé of the forgery in the fifteenth century. However, the Constitutum Constantini– the document itself – and the looser motif of the ‘Donation of Constantine’ became a cultural assumption, and even if its meaning and implications were not always clear, it retained a powerful hold on the debate for centuries.

Given the importance of the Constitutum Constantini and the ‘Donation of Constantine’ to western medieval developments, the announcement by De Gruyter's of a book which ‘not only reinterprets the origin of this forgery, but retells, as well, the history of its misinterpretation since the High Middle Ages’ was a promise indeed. Moreover, the publication of the book in English was also a notable feature: English contributions to the subject have been scarce, so the appearance of a work on the subject, in English, from a leading German medievalist closely involved in the continental debate, was to be awaited with interest by anyone with research or teaching interests requiring them to deal with history of the Donation. Or, indeed, by anyone with a general interest in the medieval papacy and medieval society.

There is certainly much in Johannes Fried's new book which is of great use and interest. The volume is slim (the main text 114 pages, the appendix by Wolfram Brandes adding a further 13), but that in itself is obviously no measure of merit: short works can often be more comprehensive and informative than lengthy tomes. Moreover, the book includes in its appendices a lengthy bibliography, the text of Horst Fuhrmann's edition of the Constitutum Constantini, and the version of the Constitutum given in Emil Friedburg's edition of Gratian's Decretum– both the latter with English translation.

Turning to the text itself, the book is divided into two main areas. The high point of the first is chapter III: ‘The origin and fate of the “Donation of Constantine” in the High Middle Ages’. Here, Fried is avowedly concerned more with the Donation (the idea) than the Constitutum (the text), although there is much overlap. He looks at a range of aspects of the Donation, from the eleventh century onwards: how it was viewed, interpreted, altered, applied and questioned. A central preoccupation is with the dual process by which the text of the Constitutum was emended to increase the scope of its claims, while the popular conception of the Donation went yet further. Fried sees Leo IX's letter to Michael Keroularios in 1054, which used an altered version of the text, as a key turning-point, opening the way for later developments. By the time of the Reformation both the common conception of the Donation and the text of the Constitutum had progressed far beyond the original forgery. However, Fried also examines the other side of the coin: the extent to which the development of both Donation and Constitutum was accompanied by extensive criticism, debate and scepticism; the reluctance of the papacy itself to use it officially, because of its dangerous implications; the early acceptance – before Valla – of many influential members of the curia that the document was a forgery. Chapter III thus gives a fast-moving introduction to the Constitutum and the Donation through the centuries.

The second main area covered by the book, which comprises the bulk of the text, is rather different. In chapters IV, V and VI Fried develops the thesis of the book: his argument concerning the origin of the forgery, the milieu in which the text itself was formed. He posits that the forgery was produced in the 830s, in Frankish circles, in the same milieu as the pseudo-Isidorian decretals, designed for use in confrontation between the papacy and Louis the Pious. This goes against more traditional arguments which place the forgery in eighth-century Rome. Chapters IV and V discuss the wording and original intent of the document. Fried sees nothing in the wording to indicate that it was necessarily a Roman construct – the various elements could equally have been available to a forger working elsewhere – and identifies a number of discrepancies which he regards as proof that it could not have been written in Rome. Discussing the original intent of the document, Fried looks at the term potestas et dicio– the original wording used by the Constitutum to describe the powers accorded to the papacy by Constantine – and concludes that in the eighth and ninth centuries this primarily designated the spiritual and ecclesiastical authority of a bishopric. Thus the intent of the forgery was to establish extensive spiritual authority, not to support papal secular power other than in the city of Rome itself. Having cleared the ground in this way, Fried then moves on in Chapter VI to present his proposed solution to the problem: first he explains how the term Palatium Lateranense, used in the document, suggests a ninth-century Frankish context; then he continues with in-depth discussion of the activities and personages associated with the monasteries of Corbie and St-Denis in the ninth century, their role in papal-imperial confrontation, and the connections with pseudo-Isidore, in order to illustrate his proposed background to the forged Constitutum.

Thus Professor Fried's book packs into a small space a wealth of discussion and information. It presents a closely-argued thesis concerning the origins of the forgery, together with an overview of its later history. It is particularly noteworthy for the strong sense it conveys of the evolution of the motif, and of the importance of distinguishing between the text itself and the popular conception of its meaning.

However, there are a number of points which perhaps should be made for the benefit of potential readers. It must be emphasised that although the book gives the impression of containing introductory material, it is not designed with this in mind: it makes no real attempt to make its presentation accessible. This, unfortunately, is at times coupled with a lack of clarity: the book is highly allusive, and often leaves the reader in doubt as to the purpose, context or impact of what has been said. In a book of this length, this is surprising. If anything, its brevity should suggest lucid, high-impact writing: but the result is in fact a work of considerable obscurity. One might be forgiven for thinking that in the circumstances a longer work might have been desirable, enabling more explanation, where necessary, of the complexities involved.

These problems are, moreover, compounded by the use of English. While the translation is often very good, there are also frequent errors, of grammar, punctuation, and even actual wording, not to mention copious minor slips which should have been removed at proofreading stage. This is particularly worrying, given that extracting the meaning from the text often requires very close attention to detail: slight errors of grammar and language could certainly lead to bemusement, at times even serious misunderstanding. I hesitate to make too much of this, since it could suggest excessive pedantry: but questions need to be raised over the editorial process which allowed for such discrepancies. Wolfram Brandes' contribution in particular suffers from a lack of proper English-language editing.

In conclusion, Fried's book is certainly an important scholarly contribution, much to be welcomed. However, there is a sense in which an opportunity here has been missed. Publication in English offered the opportunity for presenting a specialist scholarly field to a wider academic audience – an audience which undoubtedly exists, given the importance of the subject. To a certain extent, Fried's book has achieved this: but it could have done so with less allusion and more structured explanation.