Now it happens that from the 20th year of the reign of Artaxerxes (as it is given in Ezra among the Hebrews), which, according to the Greeks, was the 4th year of the 80th Olympiad, to the 16th year of Tiberius Caesar, which was the second year of the 102d Olympiad, there are in all the 475 years already noted, which in the Hebrew system make 490 years, as has been previously stated, that is, 70 weeks, by which period the time of Christ’s advent was measured in the announcement made to Daniel by Gabriel.
~Africanus, 'The Extant Fragments of the Five Books of the Chronography of Julius Africanus', fragment XVIII (from Syncellus, 'Chronicles'), in Roberts,Donaldson & Coxe (eds.), 'The Ante-Nicene Fathers Vol. VI : Translations of the writings of the Fathers down to A.D. 325', p. 138