Timaeus (Ancient Greek: Τιμαῖος; c. 345 BC – c. 250 BC) was an ancient Greek historian.
He was born at Tauromenium (modern Taormina) in Sicily. Driven out of Sicily by Agathocles, he migrated to Athens, where he studied rhetoric under a pupil of Isocrates and lived for fifty years. During the reign of Hiero II he returned to Sicily (probably to Syracuse), where he died.
While at Athens he completed his great historical work, the Histories, probably some 40 books. This work was divided into unequal sections, containing the history of Greece from its earliest days till the first Punic war. The Histories treated the history of Italy and Sicily in early times, of Sicily alone, and of Sicily and Greece together.
Timaeus devoted much attention to chronology, and introduced the system of reckoning by Olympiads. In order to plot chronologies, he employed the years of Archons of Athens, of Ephors of Sparta, and of priestesses of Argos. This system, although not adopted in everyday life, was afterwards generally used by the Greek historians.
Timaeus can claim to be the first to recognize in his work the importance of Rome, which was gaining power.
Very few parts of the elaborate work of this historian were preserved after Antiquity:
Timaeus' work was however well spread in antiquity, as many ancient historians and other writers refer to it, and/or based their work on his writings.