We could also try to make an explicit Game of Thrones reference, if it's not too repetitive: "Oberyn Martell and the Mountain from *Game of Thrones* could have fought in a trial by battle as late as 1818," or "*Game of Thrones*' Tyrion could have requested a trial by battle as late as 1818."
*Game of Thrones* there would be linked to the show's page (that should drive up views).
Sorry, if I actually watched GoT I would have thought of this before.
--Ed