"Gates of Fire" by Steven Pressfield
I am almost done with this book. It is a very entertaining book about the 300 Spartans and a few thousand Allies last stand against 250,000 Persians at the choke point called Themopylae(Hot Gates)in 480BC. It's fiction, but very well written. It captures the "Warrior Ethic" very well. I highly recommend it. The language can be crude in a "one of the boys" sense.
"This is for all you new people: I only have one rule. Everyone fights.
No one quits. You don't do your job, I'll shoot you. You get me?"
- Lieutenant Jean Rasczak