On Laudator Temporis Acti, Michael Gilleland points to the interesting parallel between Mark 6.17-29 // Matt. 14.3-12 and "a remarkably similar episode from the life of Lucius Quinctius Flaminius, consul in 192 B.C., expelled from the Senate by Cato the Censor in 184 B.C." The story is found in Cicero, Livy, and Plutarch and Michael has the texts handy:
A Head on a Platter
Michael notes that the parallel is not mentioned in the commentaries available to him. It is, however, occasionally mentioned in recent literature, e.g. according to Ross Kraemer, Kathleen Corley and John Dominic Crossan both claim that Mark invented the story on the basis of the one about Lucius. See Ross Kraemer, Herodias I in Carol Meyers, Toni Craven and Ross Kraemer, Women in Scripture: A Dictionary of Named and Unnamed Women in the Hebrew Bible, the Apocryphal/Deuterocanonical Books, and the New Testament (Grand Rapids: Eerdmans, 2001): 92-4.