Yes, it is another war book. This one, however, is about the Battle of Thermopylae. At least the book's cover says that it is "an epic novel of the Battle of Thermopylae". But it is really about the Spartans and Greece in general, and what it was like to live in that time and be a part of that community. The story is told by Xeones, a greek squire who served a Spartan at the Battle, though he was not Spartan himself. He is only one of two survivors of that Battle, and he is only alive because the god Apollo wishes Emperor Xerxes to hear the tale of the Spartans.
This is the same story that is told in the graphic novel and movie 300, though this story is different. Only 300 Spartans leave their city to fight at the Gates, but they are joined by their other allies of Greece, which bring the numbers up to around 4000. That is still nothing compared to the Persian army of hundreds of thousands, but it is more than just the 300 Spartans. However, the Spartan king, Leonides, does release the surviving allies after two days of battle, leaving the remaining 100+ Spartans to fight alone.
Xeones begins his story by telling of his life before his city is destroyed by the Argives. He and his cousin survive and flee with one of their servants, and live in the wild for a year or two before separating. Diomache heads to Athens while Xeones heads for Sparta. He is accepted among them and serves as a squire, first to a youth his age named Alexandros, and later to the warrior Dienekes. Xeones' tale switches back and forth between his telling of the actual battle, and of other events in the years prior to that. It is Xerxes desire to know more about the Spartans who met his hundreds of thousands of Persians in battle, and so the reader gets to hear all sorts of details about their lives as well.
The best thing about this book is the in depth descriptions that Pressfield gives. He spends multiple chapters just telling of the details of the two and a half days that the Spartans and their allies stand against the Persian army. He can spend a paragraph describing a patch of mud. It's phenomenal. He brings that same descriptive power to his characters. They are fully realized, for the most part, and he obviously cares for them greatly. This is a fantastic book for anyone who enjoys history or epic battles. I even enjoyed it, and I generally dislike stories of war. But this one brought something for everyone.