Trial by combat and 'The Last Duel'
By the way, apropos trial by combat, I thought I'd recommend again "The Last Duel," a history book by Eric Jager (a UCLA English Department professor, but one whom I've only met a few times).
The book is about the last judicial trial by combat authorized by the French central government, in 1386; it seems quite thoroughly researched, but it's also a page-turner. It's got friendship gone sour; a battle to the death; a complaining witness (the wife of one of the combatants, who had accused the other of rape) who would face immediate burning at the stake (on the grounds that she had been proved a perjurer) if her husband and champion was defeated; and a battle scene that shocked even me, after all the battle scenes I've read about and watched in movies.
This would make a great historical movie, it seems to me; but in any case, it should be a great gift for your history buff friends. (And, no, I'm not getting a penny from this plug.)