Charlemagne’s repeated campaigns and final conquest of Saxony over the course of the later 8^th and early 9^th century received enormous attention in contemporary sources and concomitantly from scholars ever since the beginning of university-based historical inquiry in the 19^th century. The great length of the effort to integrate Saxony politically within the Regnum Francorum (772–804), which required a full generation, and the concomitant extension of the Christian ecumene to a region that had not been part of the Roman Empire, have both been a primary focus of scholarly attention. In this context, most scholars have argued that even if Charlemagne’s initial campaigns in Saxony in the early 770s were not driven primarily by religious concerns, the war of conquest quickly took on a strong Christian patina. As a consequence, it is generally agreed, Charlemagne sought by the 780s both to convert the Saxons to Christianity and to establish a full ecclesiastical infrastructure of bishoprics and parishes throughout the Saxon region. It is also generally agreed that the eight bishoprics within the Saxon region were fully organized by early in the reign of Charlemagne’s son, Emperor Louis the Pious (814–840).

In the published version of his dissertation, completed at the University of Bonn under the direction of Professor Theo Kölzer, Andreas Mehdorn seeks to overturn the scholarly consensus regarding the conversion of the Saxons and particularly the establishment of an institutionalized church in the Saxon region during Charlemagne’s reign. Mehdorn begins with the claim that much of the state of the question regarding the institutionalization of the Saxon church is based on analyses of privileges granted to the Saxon bishoprics by Emperor Louis the Pious. Mehdorn emphasizes, however, that the recently published edition of Louis’ charters by Theo Kölzer (2016) shows that almost all of these privileges, and all of the early ones, are forgeries. The first legitimate privilege is for the bishopric of Paderborn, issued in 822. The next two surviving legitimate charters, for the bishoprics of Verden and Osnabrück, were not issued until the reign of Louis the German (840–876), the son of Louis the Pious. On the basis of this finding, Mehdorn seeks to move the establishment of the institutional church in the Saxon region from the reigns of Charlemagne and Louis the Pious, to the reign of Louis the German.

In place of an institutional church, with fixed diocesan and parish boundaries, Mehdorn envisions a missionary church operating in the Saxon region from the period before the accession of Charlemagne in 768 well into the reign of Louis the Pious. The model for this missionary church, Mehdorn argues, was provided by Anglo-Saxon missionaries who operated in the German-speaking lands under the auspices of Charles Martel (715–741), and his sons Carloman (741–747) and King Pippin I (741–768). Mehdorn adds that the Anglo-Saxon missionaries were, themselves, influenced by Irish ecclesiastical organization, which was based on monasteries rather than bishoprics. The key point of comparison that Mehdorn draws between Ireland and the Saxon region is the supposed lack of population centers that could be understood by contemporaries as civitates. In this context, Mehdorn emphasizes the canonical requirement for an episcopal seat to be established in a civitas.

Following a brief introduction, which provides the historical and historiographical background for Mehdorn’s discussion of what he sees as the missionary church in Saxony, the volume is organized in three chapters. In the first of these chapters Mehdorn sets out the argument for identifying ecclesiastical activity in Saxony from ca. 750–850 as the work of a missionary rather than an institutional church. He draws almost exclusively on written sources, and argues, incorrectly as will be discussed below, that there is no archaeological evidence that would help to illuminate the questions that he seeks to address. Throughout this introductory chapter, Mehdorn draws extensively on the published work of Theo Kölzer for a late dating of all ecclesiastical institutions in Saxony. Notable, however, is the lack of attention to scholarship in English on Charlemagne’s conquest of Saxony and the institutional structures that he developed there. Missing, for example, are crucial studies by Christopher Landon, Bernard Bachrach, and Eric Goldberg.

The second chapter, which is the lengthiest of the volume, provides a prosopographical catalog of 50 missionaries, who can be identified on the basis of written sources to have operated within the Saxon region from the mid-8^th to the mid-9^th century. For each of the alphabetically listed missionaries, Mehdorn discusses the historiographical tradition treating this figure, the sources which mention the individual, and the missionary activities that the individual is reported to have carried out. These individual prosopographical entries vary quite considerably in length, depending upon the available source materials and concomitant scholarly discussion. On the basis of his investigations of these missionaries, Mehdorn argues that nine of them, namely seven men included on the early bishop list from Verden and the first two ostensible bishops from Osnabrück, never existed.

In chapter three, Mehdorn provides a systematic evaluation of the information developed in the individual biographies from chapter two. He divides his analysis into nine parts, considering the available source materials, the origins of the individual missionaries, the education of the missionaries, how the missionaries were recruited, the scope of their missions, their missionary practice, their relationships with secular authorities, as well as their deaths and memorialization. He also includes a section that is focused on the question of what it meant to be a missionary bishop. Mehdorn reaches a number of valuable conclusions in this section, including the important role that monasteries played in training future missionaries, and the central role played by German-speaking missionaries in preaching Christianity to various gentes whose Germanic languages and dialects were similar to their own.

However, many of the conclusions drawn in this section are circular. Mehdorn’s arguments all start from the assumption that the church in Saxony must have been missionary in nature and not institutional, and he consistently excludes any interpretation of the evidence that suggests the existence of an institutional church during the reign of Charlemagne. For example, Mehdorn dismisses the state of the question regarding texts such as the »Annals of Lorsch«, which comment specifically on the division of the Saxon region by Charlemagne among bishops and priests for the purpose of both preaching and baptizing the inhabitants. Most scholars have seen this text as providing evidence for the establishment of an institutional church. Mehdorn rejects this interpretation because of his a priori view that in the absence of early privileges for bishoprics, these bishoprics simply could not have existed as institutional entities with established boundaries.

Mehdorn argues in this context that there was no reason during Charlemagne’s reign for the establishment of bishoprics with fixed boundaries because boundaries were only necessary when there were competing claims in play. Mehdorn denies that such competing claims existed at this early a date. However, when discussing the early church organization in the Saxon region Mehdorn completely ignores the imposition of tithes, and consequently the interest of ecclesiastical officials in collecting them. The neglect of this issue is problematic because it was during Charlemagne’s reign that tithe collection became a central concern of the government. Moreover, the imposition of tithes was a major element of Alcuin’s complaint about Charlemagne’s efforts to establish Christian institutions in Saxony. In light of Charlemagne’s efforts to compel tithe payments throughout the empire, and Alcuin’s explicit complaints about this practice in Saxony, it would seem that we have clear evidence of a reason for bishops and the Carolingian government to want to establish diocesan boundaries. In this context, although Mehdorn does comment on Alcuin’s criticism of Charlemagne in broad terms (p. 18), he does not address the specific issue of tithes.

In a similar vein, Mehdorn does not discuss either the decision by the Carolingian government to impose a comital structure in the conquered Saxon region from a very early date, or the concomitant development of a politico-military infrastructure there during the final two decades of the 8^th century. As is true with regard to the problem of tithe payments, addressing these issues would have required Mehdorn to consider that the Carolingians had a much clearer idea of both the physical and political topography of the Saxon region, from a much earlier date, than the terra incognita required by his ad hoc missionary model, with missionaries wandering about uncharted hinterlands in search of converts.

Finally, Mehdorn’s decision not to address the considerable corpus of archaeological material available for both pre-conquest and early conquest-period Saxony is highly problematic. First, numerous archaeological studies call into question both the putative lack of population concentrations that were consistent with civitates as well as the supposed lack of hierarchical political organization among the Saxons. These are two of the factors which Mehdorn argues inhibited the early development of an institutional church. One might point here to the important studies by Matthias Hardt regarding the construction by the Saxons of a series of frontier fortifications directed against the Franks, which date back to the early 8^th century. These fortifications illuminate both considerable population centers and also a political structure capable of mobilizing very extensive labor resources.

Overall, Mehdorn’s study provides a valuable prosopographical account of the missionaries, who were involved in the conversion of the Saxons, as well as their continued integration into the broader Frankish church over the course of the 8^th and 9^th century. He also has done a service in drawing attention to the insights provided by the edition of Louis the Pious’ charters by Theo Kölzer and the problematic use of forgeries to make arguments about the reigns of Charlemagne and Louis the Pious. This point would have been enhanced, however, if Mehdorn had provided more detail about both the dates and purposes of these forgeries rather than simply citing earlier studies by Kölzer to insist upon a late dating of Saxon bishoprics and monasteries. Mehdorn’s overall effort to challenge the state of the question regarding the development of the institutional church in Saxony runs into problems, however, when he disregards other sources of information that can illuminate this topic. These include not only narrative accounts and letters such as those by Alcuin regarding tithes, but also the very extensive material sources of information, which attest to the highly organized nature of Saxon society before the conquest, and the rapid re-organization of this society on Frankish terms during Charlemagne’s reign.