Persians under Xerxes
had both a land and a sea force with which they attempted to defeat those Greeks who wouldn't willingly accept Persian domination, as many Greek city-states
had already done. So the Battle of Thermopylae included a land and sea component. The 300 Spartans led by the Spartan King Leonidas
met the Persians by Thermopylae
, while the naval forces, which were under the Athenian Themistocles
, met them by sea, most importantly at Artemisium.
I haven't read Pressfield's Gates of Fire. Although it's fiction, a reader said he thought it should appear here. I disagree, but thought I'd pass it along, anyway.
The British title for this book, The Year of Thermopylae
(London, 1980), is much more descriptive since the book covers events leading up to and including Thermopylae. A military historian, Bradford makes sense of the complicated maneuvers and does a very thorough background on all components of the battle, from the three rows of trireme rowers to an analysis of the (less than) treachery of the traitor Ephialtes to an explanation of the only apparent megalomania of Xerxes.
Peter Green does a masterful job of detailing the Persian Wars, especially for those who have already read Herodotus carefully. The maps are awful (see Bradford, instead) unless you are interested in seeing what's there today. Green explains that it was the naval battle at Artemisium, where the Greeks may disputably be considered the victor, that Pindar described as "the shining cornerstone of freedom" because Xerxes had lost too many of his ships to divide them, send half to Sparta, and so conquer the Greeks.
is one of many books and articles on the Spartans Paul Cartledge has written. It is not just about the Persian Wars, but describes the Spartans in general and Leonidas in particular so that it is understandable why he would fight to the death at Thermopylae. It also explains relations between Sparta and the other Greek city-states. The book is nicely illustrated and accessible to readers who haven't read Herodotus.
Cartledge's Thermopylae came out November 2006. I haven't yet read it.