Anonymous, Life of Aeschylus ch. 8
ἀπῆρεν δὲ ὡς Ἱέρωνα, κατά τινας μὲν ὑπὸ Ἀθηναίων κατασπουδασθεὶς καὶ ἡσσηθεὶς νέωι ὄντι Σοφοκλεῖ, κατὰ δὲ ἐνίους ἐν τῶι εἰς τοὺς Μαραθῶνι τεθνηκότας ἐλεγείωι ἡσσηθεὶς Σιμωνίδηι· τὸ γὰρ ἐλεγεῖον πολὺ τῆς περὶ τὸ συμπαθὲς λεπτότητος μετέχειν θέλει, ὃ τοῦ Αἰσχύλου, ὡς ἔφαμεν, ἐστὶν ἀλλότριον.
He left Athens for the court of Hieron, as some say because he was vexed with the Athenians because of his defeat by Sophocles, then a young man; according to others, it was because he had been defeated by Simonides in an elegy for those who died at Marathon. For elegy requires much subtlety as regards the treatment of emotions, which, as we said, is alien to Aeschylus.