The History of the Peloponnesian War by Thucydides 431 BC. Thucydides, an Athenian, wrote the history of the war between the Peloponnesians and the Athenians, beginning at the moment that it broke out, and believing that it would be a great war and more worthy of relation than any that had preceded it. This belief was not without its grounds. The preparations of both the combatants were in every department in the last state of perfection; and he could see the rest of the Hellenic race taking sides in the quarrel; those who delayed doing so at once having it in contemplation. Indeed this was the greatest movement yet known in history, not only of the Hellenes, but of a large part of the barbarian world