Generally considered the greatest historian of ancient Greece, his main work was 'The History of the Peloponnesian War', and is the only work of his that has been preserved.
It is known that Thucydides was born in Alimos, a municipality within Athens, and that he contracted the plague in 430 BC but recovered from it. He was well to do from his inheritance of gold mines in the region of the Strymon River, in northern Greece.
He attended classes given by the Sophists and carried out meticulous historical research. One of his teachers was the philosopher Anaxagoras. He was elected to the post of general in 424 BC, and put in command of the Athenian fleet in the region of Thrace, opposite the island of Thasos, but failed to prevent the Spartan general Vrasidhas from capturing the city of Amphipolis, which resulted in his recall, with charges of treason leveled against him, and was exiled for twenty years, which he spent mostly in Thrace, where his goldmines were, though he also travelled to the Peloponnes and Sicily (including Syracuse).
He was allowed, even as an exile, to meet and converse with the Spartans and their allies and hence learn their views about the war. After the end of the war, he returned to Athens, in 404 BC, though he spent his last years again in Thrace, where he continued his writing work, and died suddenly from unknown causes.
His history of the war was not divided into books, nor did he give it a titled, which was left to the ancient grammarians.
The war actually lasted twenty years, though he included the seven years after the peace of Nicias in 421 BC, and thus reported it as a 27 year event. He was the first historian to proceed in a scientic manner in the collection of historical data and the interpretation of historical events, believing strongly in the duty of the historian to verify his material.
He relied on first hand wintnessing of events, or, if this were not possible, cross checking information received second-hand with as many sources as possible. He also used official records such as city archives , treaties and pacts, etc. which he often quoted directly, word for word.
His view of history excluded surpernatural intervention in the affairs of humans, or moralizing about historical events, which he saw as the result and reflection of human nature, which was bent on personal gain and power.
His life and writings had a great influence on those who followed him, and his credibility as an historian went unquestioned.