All the accounts I have read claim that the Spartan battle with the Persians at Thermopylae was significant due to delaying the Persian army, allowing the Greeks city states to form a combined army. A friend claimed there was a letter from a Persian soldier which indicated that the Persians were demoralized by the thought of facing a Greek army which included circa 2000 Spartans. Does any history buff Posting here have information relating to the above.
This covers the basics: http://www.ancient.eu/thermopylae/ A more story telling approach is this: Historical tales by Charles Morris https://books.google.com/books?id=E2A9AAAAYAAJ&pg=PA144&source=gbs_toc_r&cad=3#v=onepage&q&f=false