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.