Why is herodotus significantin the war between the greek city states againist the Persian Empire

He gives a coherent account of the background and events. While there are exaggerations ad inconsistencies (he delivered his account at a series of paid lectures in Athens forty years later, and he was not an eye-witness), his account is based on some detailed research and consultation with survivors of the war, and is by far the best we have. Other accounts are incomplete and of very low reliability.