Near Dinas Emrys, Owain ap Macsen fought with a giant. As they were equal in fighting with tree trunks, Owain leapt up a hill on the other side of the river and cast a stone which fell at the feet of the giant, who cast it back. They then tried wrestling. Owain became enraged, threw down the giant, who shattered a huge stone in the fall and a piece entering his back, he was killed. In dying he crushed Owain to death.
From T Gwynn Jones’s “Welsh Folklore and Folk Custom” (1930), from a Welsh 1875 source.