No further danegeld was collected in Frisia until late in the reign of Louis the Pious (died 840). In 836 some Northmen, having burnt Antwerp and the marketplace at Wintla, agreed to leave on the payment of some tribute, the amount of which the "Annales Fuldenses" do not specify. In 837, either because the Frisians were unprepared or defected from their Frankish overlords, some Vikings managed to land on Walcheren, capture several counts and other leading men and kill them or hold them for ransom. They then proceeded to exact a "census" wherever they could, funnelling an "infinite" amount of money "of diverse kinds" into their coffers. They then moved to the mainland, where they assaulted Dorestad and extorted a tribute from the population of the region before leaving. This event is recorded in the "Annales Fuldenses", "Annales Bertiniani", "Annales Xantenses", and the "Vita Hludowici imperatoris" of Thegan of Trier. In 846, during the reign of Louis's son Lothair I, the Vikings compelled the Frisians to collect a "census" to pay them off. The "Bertiniani" and "Xantenses" annals record how Lothair, though aware of the outrage, was unable to stop it, and the Vikings left Frisia laden with booty and captives.