As other people have already mentioned, diamonds shatter too easily to be effectively used in most armor. You could maybe use it to some effect in scale armor, but I wouldn't trust it.
Like in the case of armor, diamonds are simply too easily fractured to be used in a medieval-style broadsword. However, if you are willing to bring ...
AlexP beat me to it in comments again, but I am used to that. It actually is kind of reassuring now.
So what old game to play with dice? How about backgammon?
Backgammon dates back to about 5,000 years, and is said to have
originated from somewhere in the Middle East ...