Thucydides & Xenophon 
The History of the Peloponnesian War & Hellenica 
The Complete History of the Peloponnesian War and Its Aftermath

The History of the Peloponnesian War is a historical account of the Peloponnesian War (431–404 BC), which was fought between the Peloponnesian League, led by Sparta, and the Delian League, led by Athens. Thucydides’ account of the conflict is widely considered to be a classic and regarded as one of the earliest scholarly works of history.
Hellenica is direct continuation of the History of the Peloponnesian War. There is virtually no transition between the two works, to the extent that the opening words of Hellenica are translated as 'After this’, or sometimes 'Following these events’. The Hellenica recounts the last seven years of the Peloponnesian war, as well as its aftermath. Many consider this a very personal work, written by Xenophon in retirement on his Spartan estate, intended primarily for circulation among his friends, for people who knew the main protagonists and events, often because they had participated in them.