Saxo Grammaticus,
The Danish History — Book VII
“ And when Frode thought that they were possessed, he gave up his purpose, thinking it shameful to attack with the sword those who seemed to be turning the sword against themselves. But he was burned to death by them on the following night, and was punished as befitted a fratricide. For they attacked the palace, and first crushing the queen with a mass of stones and then, having set fire to the house, they forced Frode to crawl into a narrow cave that had been cut out long before, and into the dark recesses of tunnels. ”
