"Though after all your Xenophon and Thucydides I dare say there are not many young people better versed in military tactics"

 Ancient Greek historians whose books recount the wars of Ancient Athens.

Thucydides (c.460-395 B.C.) wrote the famous History of the Peloponnesian War, which is still studied in military schools today, and is said to be the favourite reading of neoconservative American politicians. The book describes the history of the war between Sparta and Athens in the fifth century B.C.

Xenophon (c. 430–354 B.C.) was an Ancient Greek writer and soldier. He was a contemporary admirer of Socrates. His book Hellenica follows on directly from events in Thucydides' History of the Peloponnesian War, to the extent that it begins "Following these events..."