Tenth-century Normandy is a world fraught with dangers for the historian. The Vikings who founded Normandy were illiterate, and left no account of their own. What information we do have comes from the neighboring Franks, who distrusted (and in many cases hated) the invaders from the north, and left strongly biased accounts that tended to view the Vikings in Frankish terms. Furthermore, the Viking settlement at Rouen falls, annoyingly, during precisely a period when no major Frankish historians were active; several thorough German annals end around 900, and Flodoard of Reims, our best source for the early years of Normandy, only begins in 919. And during the tenth century, there are several periods of years or decades where nothing that occurred in Normandy was of interest to the Frankish writers, and so we know precious little of those times. As a result, since the information is so scanty, the danger is great for historians to read things into early Norman history that might not actually be there.
I should explain, for the sake of full disclosure, where I stand on two issues that color the views of every Norman historian. The first of these is Dudo of Saint-Quentin, a Frankish writer of the early eleventh century who purported to write a History of the Normans under the first three rulers, from the beginning until 996. For a long time, historians have discounted Dudo's work in fairly strong terms, recognizing that much of what he says is inherently implausible and that his book was strongly colored by the way he wished to portray the Normans of his own day. But it is very difficult to reject Dudo, since the vast majority of the information we have on tenth-century Normandy comes from him, and indeed, even those historians who reject him tend to tell a story influenced by him in at least the broad outline. Recently, some historians have begun to appreciate Dudo not as an historian of the modern sort, but in his own context, as a Carolingian-educated writer of the eleventh century trying to make points about the contemporary situation, and thus a good source for eleventh-century Norman history, not tenth-century events. And a school of thought is developing in France that is trying to "reform" Dudo's reputation, and give much greater credence to his history. I am not in this school, and in what follows I will use Dudo only with the very greatest caution, when I think there are very strong reasons to believe his version of a particular event. For the most part, this will be early Normandy without Dudo.
The second issue is the fundamental nature of early Normandy. The dispute is best seen in the works of the two leading English-language Norman historians of recent years, David Bates and Eleanor Searle. To Bates, the Vikings of Rouen very quickly assimilated into Frankish culture and political structures, so that within a generation or so Normandy was in effect a territorial principality on the Frankish model, and tightly integrated into the Frankish world. Searle, on the other hand, saw the Vikings of Rouen as Vikings first and foremost, who maintained their cultural distinctness throughout the tenth century and indeed well into the eleventh, only fully adopting Frankish ways (and then only imperfectly) during the reign of William the Conqueror (ruled 1035-1087). I think Searle is overall more convincing on the tenth century (and to be fair, Bates devotes only a few pages of his book to that period), and Bates for the eleventh, but I also think there is room for compromise; some Vikings assimilated more quickly than others, and some Frankish ways were adopted more quickly than others. But while I see the early Norman rulers as being, in effect, ahead of the assimilation curve, I still do not view Rollo (c.911-c.930) or William Longsword (c.930-942) as primarily Frankish royal officials; they were still in many ways Vikings, and even Richard I (942-996) had his Viking side.
A few words on terminology: The words we use to describe people color strongly our perceptions of them, and nowhere are the dangers of this greater than in tenth-century Normandy. It is, for example, customary to speak of Normans and Vikings, and thus draw a sharp linguistic boundary between them. Yet "Norman" (lat. Northmannus) is simply the medieval Latin word for Viking; Frankish writers told of Northmanni not only in what became Normandy, but also elsewhere in the Frankish realms and in Scandinavia as well. To the Franks, there was no distinction between the inhabitants of Rouen on the one hand, and the guys in the long-boats who sailed from Norway to pillage the Frankish countryside; they were all equally Northmanni (or, in the somewhat harsher word of Richer of Reims, a late-tenth-century historian, they were all equally "Pirates," even after the Northmanni had been settled at Rouen for a century and were becoming an accepted part of the Frankish political landscape). Thus, to write of Normans and Vikings is to create an artificial distinction that would not have been recognized by contemporaries, and instead I will always use "Northmen." Likewise, the word "Normandy" has very strict connotations for us--it is the territory associated with the 11th- and 12th-century duchy, extending from Eu in the east to Mont-Saint-Michel in the west, with a clearly-defined southern frontier. But in the tenth century, Normandy (lat. Northmannia) mean Viking-land, or Northmanland. As late as the 1030s, Adémar of Chabannes, a clerical writer in Aquitaine, used Northmannia equally to refer to the future Normandy, other Northman settlements in the Frankish realm, and the Northmannic homelands of Denmark and Norway. Northmannia was simply a place where Northmen lived, and was not in any way associated exclusively with what we consider Normandy (in fact, the one time Adémar uses Northmannia to mean Normandy is also the one time he feels the need to explain what he means--"In that Northmannia that previously was known as Neustria"). During the tenth century, the territory that would eventually become Normandy was never united under the control of any one man or dynasty, and it would be the task of the eleventh century to establish finally those boundaries.
Furthermore, the remarkable family of William the Conqueror's ancestors is often referred to as the dukes of Normandy, or more recently the counts of Rouen. But they are known to have held neither of these titles during the first decades of their existence. The only term used regularly to describe them in contemporary writings is princeps, or prince. But we have to call them and their lands something, so I will refer to Rollo and his descendants as the Rollonids; for the tenth century I will call the land where the Northmen lived Northmanland, and the territory ruled by the Rollonids will be called the Rollonid Principality.