 Significant historians of the period were Timaeus, Polybius, Diodorus Siculus, Dionysius of Halicarnassus, Appian of Alexandria, Arrian, and Plutarch.The period of time the cover extended from late in the 4th century BC to the 2nd century AD.Eratosthenes of Alexandria wrote on astronomy and geography, but his work is known mainly from later summaries.