(Two motifs in this story, the champion's portion and the beheading challenge, are mentioned by the Greek writer Posidonius as practices of the ancient Celts. The beheading challenge is also central to the Middle English Arthurian poem Sir Gawain and the Green Knight.)
Diogenes Laertius mentions a work of his wherein he compares Posidonius with Panaetius in arguing from physical principles