It is a point of some interest to the historian of the social and intellectual development of Athens to determine, if possible, the exact dates between which the philosopher Anaxagoras made that city his home. As everyone knows, the tradition of the third and later centuries was not uniform. The dates from which the Alexandrian chronologists had to arrive at their results may be conveniently summed up under three headings, (a) date of Anaxagoras' arrival at Athens, (b) date of his prosecution and escape to Lampsacus, (c) length of his residence at Athens, (a) The received account (Diogenes Laertius ii. 7), was that Anaxagoras was twenty years old at the date of the invasion of Xerxes and lived to be seventy-two. This was apparently why Apollodorus (ib.) placed his birth in Olympiad 70 and his death in Ol. 88. I, thus giving the years 500–428 B.C. of our reckoning, (ib.) The further statement of Apollodorus that Anaxagoras ἤρξατο ϕιλοσοϕεῖν ⋯π⋯ Καλλίον has given rise to discussion; but when we remember that Demetrius of Phalerum had made what ‘Diogenes’ regards as an equivalent statement in his register of archons, and had said that Anaxagoras was twenty years old at the time, I think there can be no doubt of the meaning. Demetrius had clearly mentioned something about Anaxagoras which was looked on as giving the date at which he ‘began to philosophize,’ and had given his age at the time. The natural interpretation is that Demetrius mentioned the year of Anaxagoras’ arrival at Athens, and that this was taken as the time at which he ρξαtο φιλοσοφεlσ And it is further reasonable to suppose that this date was the source of the further statement of Demetrius, that Anaxagoras was born in or about 500 B.C. We may, I think, infer that Demetrius recorded the arrival of Anaxagoras in Athens under the year 480, giving his approximate age at that time.