In 1070 Hereward certainly participated in the anti-Norman insurrection centred on the Isle of Ely. In 1069 or 1070 the Danish king Sweyn Estrithson sent a small army to try to establish a camp on the Isle of Ely. Hereward appears to have joined them. Hereward stormed and sacked Peterborough Abbey in company with local men and Sweyn's Danes. While the "Gesta" says this was after the main battle at Ely, the Peterborough Chronicle says it was before. The historical consensus is that the Chronicle's account is most accurate. His justification is said to have been that he wished to save the Abbey's treasures and relics from the rapacious Normans led by the new Norman abbot who had ousted his uncle Brand. According to the "Gesta" he returned the treasures looted from the abbey after having a vision of Saint Peter. However, the Peterborough Chronicle says that the treasure was carried off to Denmark.