When the Dannevirke was begun Ongendus was the king of the Danes. We know that he was ‘more savage than a wild beast and harder than a rock.’ This is what the missionary Willibord, who tried unsuccessfully to convert him to Christianity, says about him.
Perhaps Ongendus was the man behind the Dannevirke. In any case it must have taken a powerful leader to gather together and pay the many carpenters and other workers who were needed to build such a mighty fortress.
Kings Godfred, Harald Bluetooth (?-987) and Valdemar the Great (1157-1182) made additions to the Dannevirke.