OUR KNOWLEDGE of relations between the Franks and Frisians in the Merovingian Period largely concerns the region that Bede calls Frisia Citerior (Historia Ecclesiastica, V, 10). Unfortunately the Anglo-Saxon monk nowhere offers a definition of the region, but Alcuin, in his Vita Willibrordi, states that when Willibrord first visited Radbod, which is normally thought to have been in 690, he went to the king's castrum at Utrecht (Vita Willibrordi 5). This and the revelatory excavations of Wim van Es at the site of Wijk bij Duurstede have not surprisingly led historians to concentrate their attention on the region of Utrecht and Dorestad. The very word citerior itself implies that it is more central than the other part of Frisia defined as ulterior. This, however, is only Bede's nomenclature (Bazelmans 2009, 331). We do not know where it came from, or whether it reflected an established view. It has arguably led to a rather blinkered understanding of Frankish-Frisian relations. For a start, it is worth noting that Utrecht and Dorestad do not appear to have been the home territory of those Frisian kings about whom we know anything. Stephen of Ripon (Vita Willibrordi 27) tells us nothing about the whereabouts of Aldgisl's centre of power – but he implies that it was close to fishing grounds. As we have seen, Radbod had a fortress at Utrecht, but this is unlikely to have been ancestral land, since the castellum had been in Frankish hands earlier in the seventh century (Boniface, ep. 109). Current views have placed the centre of his power in West Frisia, perhaps in Texel or Kennemerland (van Egmond 2005; Nijdam and Knottnerus 2019). Alcuin seems to imply that his authority stretched as far as Helgoland – but unfortunately the chapters of the Life of Willibrord describing the island shrine of Fosite (Vita Willibrordi, 10–11) do not make it entirely clear whether Helgoland was part of Radbod's kingdom, or whether his reaction to the saint's sacrilege was merely a response to demands made on him by the inhabitants of the island. The only other named leader, Bubo, was killed at the Battle at the Boorne (Fredegar, Cont. 17), and appears to have had his powerbase in Westergo or Oostergo. Oostergo was, of course, the focus of Boniface's mission at the time of his martyrdom at Dokkum (see Fig. 7.1 for the principal sites referred to in this chapter).