Came across one of these books quite by accident. If you have a pre-teen kid who likes history, you could do a lot worse. It also had a few good ideas for RPG.
Tournament swords designed to break. An awesome idea for an aquatic race.
Maces wrapped in cloth, again for tournaments. Sounds like a good idea for magic object.
Also, the book I read (Dark Knights and Dingy Castles) got into the old mace/cleric controversy. Apparently, priests who wanted to go on Crusade were not allowed to 'shed blood'. In typical Catholic fashion, some would use the loophole that maces didn't cut and therefore didn't 'shed blood' (brains and bone notwithstanding).