The ferociously competitive nature of lordship and kingship in the Hiberno-Scandinavian world tends to defy general historical analysis: the source materials are heterogeneous and fragmented, and even were they fuller, the dynamics of power would still be very difficult to track. Benjamin Hudson offers a new approach by tracing the fluctuating fortunes of two families of Scandinavian origin, the Olafssons and the Haraldssons, paying keen attention to prosopography and shifts of abode. This has the advantage of bringing out the many-sidedness of their regimes: the judicious marriage-ties contracted with Celtic dynasties as well as with one other help to explain the families' resilience. Hudson shows that the Olafssons, whether acting individually or in tandem with one another, remained a force in the politico-commercial sphere of Dublin rather longer than is usually supposed. Dublin became the seat of Olaf Cuaran from 952 onwards and this formerly indigent sea-lord maintained himself on the Liffey for a generation, presiding over a vibrant emporium and manufacturing centre, before eventually abdicating and retiring to die in the monastery of St Columba on Iona. His descendants remained more or less continuously in charge of Dublin until 1046, and the prime contender for the city at that time belonged to the other main dynasty, the Haraldssons. This dynasty's ‘founding brothers’, Magnus and Godfrey Haraldsson, had established themselves on the islands and headlands of the northern reaches of the Irish Sea in the third quarter of the tenth century and they, too, profited from long-range commercial and familial connections. Hudson argues audaciously but convincingly for identifying their father with the ‘king’ or chieftain named Harald who was, until c. 954, ensconced in the region of Bayeux. If the dynasty's patriarch exercised power there for a while, this might account for the numerous links, political as well as commercial and cultural, between what emerged as the Haraldssons' ‘Kingdom of the Isles’ and Normandy in the second half of the tenth and the earlier eleventh centuries. The Haraldssons' position astride the northern Irish Sea was reinforced by an opportune alliance with the Irish high king Brian Boru, himself periodically in need of a seaborne ally against the Olafssons of Dublin.

The vitality of the links of both the Olafssons and the Haraldssons with Irish kingly families forms the background to Hudson's important re-evaluation of the battle of Clontarf. Against the conventional picture of the Irish shaking off the Viking yoke, Hudson points out that Dublin itself was neither sacked nor seized by Brian Boru's warriors: while Brian was slain, Sitric Silkenbeard long remained a player in the power-game for the city. Hudson argues that the Irish high king was acting essentially defensively, in response to the challenge to his overlordship from Sitric, Jarl Sigurd of the Orkneys, and other Viking allies whom Sitric had acquired from around Britain's coastline: ‘control of the Irish Sea trade’ was at issue (p. 97). The sudden death of Svein Forkbeard in 1014 and consequent turmoil in England seem to have adversely affected commerce in Dublin, reflected in lighter coinage, and Sitric could no longer look to a sympathetic Scandinavian potentate to his east. Conversely, once Cnut took over the English kingdom's resources, Sitric's prospects in Dublin began to brighten and from 1028 until his abdication in 1036 he was mostly on the offensive, extending his lordship in various directions. Hudson claims that Sitric became ‘a client of Cnut … in the second quarter of the eleventh century, probably by the year 1026’ (p. 126). The evidence from annals, Icelandic verses, numismatics and several English charters weighs heavily in favour of Hudson's thesis, and the fact that Sitric was driven from Dublin within a year of Cnut's death is in itself suggestive.

One of the means by which Sitric sought to legitimise his hold on Dublin was through gaining papal approval for the establishment of an archbishopric. Hudson suggests that Sitric's pilgrimage to Rome had some bearing on this, and he notes that Cnut had visited the holy city in the previous year, 1027. The Irish-born churchman assigned to the see, Donatus, remained in post continuously until his death in 1074, and he oversaw the construction of a cathedral church and amassed relics of saints from far-flung places associated with Dublin, including those of Olaf of Norway and Audoen of Rouen. Neither the residence of an archbishop nor the relics brought permanence to Sitric's rule there. But the new configuration of commercial, cultural and ecclesiastical ties could be made to work to the advantage of a capable, locally-based, operator. One such was an obscure-born prince of Leinster, Diarmait mac Maél na mbó. For some twenty years from 1052 he ruled Dublin and the other emporia along Ireland's east coast, also taking in the Irish high kingship and the Haraldssons' Kingdom of the Isles. Hudson demonstrates Diarmait's naval capability and tendency to dabble deftly in English, Welsh and also Norse affairs. He signals connections between episodes that are well-known but usually viewed in isolation, for example the flight to Diarmait's court in 1066 of two sons of Harold Godwinson with their cousin Tostig, and Lanfranc's assertion of Canterbury's primacy at the time of consecrating a successor to Donatus. The latter episode is of a piece with Lanfranc's well-known ambitions for reform and standardisation of clerical living. But his interest in affairs to the west and the far north of Britain converged with the anxieties of Anglo-Norman kings concerning ties between the Irish, the Danes and the family of Harold Godwinson. The high king who effectively took over Dublin from Diarmait, Tairdelbach, proved less inclined towards politico-military initiatives in England. But neither William i nor William Rufus could rest easy on this account. As Hudson shows, the prince who established himself as lord of Gwynned in the 1080s and 1090s, Gruffudd ap Cynan, was a Dublin-born Olafsson on his mother's side and he relied heavily on Viking and Irish ships and crews. And the principality that Gruffudd formed proved to be viable and long-lasting. Some new Hiberno-Norse configuration might yet have drawn on Dublin's resources to divide, rather than merely needle, the Anglo-Norman polity. In the event, the multiplicity of emporia on the eastern Irish coast and the resilience of the land-based kings made it virtually impossible for a sea-lord to consolidate his hegemony over Dublin. The city remained relatively easy to capture yet difficult to hold, and the Olafssons ultimately failed in their bid to regain dominion over Dublin, settling for the poorer Kingdom of the Isles. But, as Hudson implies, this owed something to the watchfulness of the Anglo-Norman kings, whose potential informants included the bishops of the Orkneys. Through comparison of the Manx Chronicle with sources relating to the Orkneys, Hudson shows that the Orkneys and Skye and the Kingdom of the Isles formed part of the same bishopric in the later eleventh and first half of the twelfth century. This, too, may count among the repercussions of Lanfranc's pastoral concerns.

The thesis of A. P. Smyth propounding the importance of the links between the Vikings of Dublin and York in the ninth and earlier tenth centuries ran into some heavy weather (notably in Peritia i [1982], 335–51). The wealth of archaeological data that has become available over the past thirty years tends to vindicate Smyth's thesis and Hudson makes good use of it, while harvesting the fruits of Quellenkritik carried out by himself and other scholars. Taking the story up to the end of the better-documented eleventh century, Hudson highlights the vitality of the affinities forged between the Olafssons and both Irish and Scandinavian dynasts. His reassessment of Sitric Silkenbeard's achievement is particularly convincing and will need to be taken into account by all future students of King Cnut's confederation. Hudson's account of the Olafssons and the Haraldssons involves numerous locales and languages, for the essence of his thesis is that one should not be thinking in terms of the linear development of royal regimes embedded in particular territories. This does not make for neatly consecutive narratives or for smooth reading, and Hudson's arguments would have benefited from more genealogical tables, lucid as his four tables are. But his demonstration of the value of long-distance trade in connecting far-flung lordships and of Christianity's role in sustaining them is both firmly based and suggestive. This work offers new, well-signposted, approaches to the study of what Patrick Wormald termed ‘the British archipelago’.