The Sack of Willibrord occurred on 4 March 868 when a warband of Danish Vikings under Bjorn Tall-Trunks pillaged the Frisian Christian monastery of Willibrord and massacred its monks.
Bjorn had sailed from Ribe to Dorestad aboard a passenger ship, bringing with him several Danish freeholders who were in search of fortune and adventure. He then recruited several Frisian natives into his warband, and he led them towards the defenseless monastery of Willibrord to seize its riches. The Vikings put all of the monks to the sword, with the priests offering little resistance. The Norse then looted a jar of expensive wine, precious amber, six casks of beer, three racks of salted fish, a bushel of apples, butter, and eight sacks of grain. They proceeded to set fire to the derelict monastery and looted 240 peningas worth of spoils, damaging their relations with the Frisians. Bjorn and his party then left Frisia for London before relations could deteriorate further.