Quintilian, Institutio Oratoria 1.10:
Let us move on to the fact that grammar and music were once conjoined. Indeed, Archytas and Euenus thought that grammar was subject to music, and Sophron (a writer of mimes, one of whom Plato approved so much that he is thought to have had his books under his pillow when he was dying) has shown that each of these men was a professor of both music and grammar. Eupolis makes the same point: he says that Prodamus taught both music and literature, and that Maricas (that is, Hyperbolus) confessed that he knew nothing of music but the literary part of it.
Even Aristophanes in one of his books demonstrates that boys were formerly accustomed to be educated thus, and among Menander’s writings we have the old man in Hypobolimaeus, who in trying to explain to a father asking his son for the reason for all of the expense which he had laid out on his education, responded that he had paid out a load of money on dancing and geometry.
Hence came the habit of passing a lyre around after dinner at parties. When Themistocles confessed that he was unable to play the instrument, he was (to use the words of Cicero) considered a bit uneducated.
transeamus igitur id quoque, quod grammatice quondam ac musice iunctae fuerunt; siquidem Archytas atque Euenus etiam subiectam grammaticen musicae putaverunt, et eosdem utriusque rei praeceptores fuisse cum Sophron ostendit, mimorum quidem scriptor sed quem Plato adeo probavit, ut suppositos capiti libros eius, cum moreretur, habuisse credatur, tum Eupolis, apud quem Prodamus et musicen et litteras docet, et Maricas, qui est Hyperbolus, nihil se ex musice scire nisi litteras confitetur.
Aristophanes quoque non uno libro sic institui pueros antiquitus solitos esse demonstrat, et apud Menandrum in Hypobolimaeo senex, qui reposcenti filium patri velut rationem impendiorum, quae in educationem contulerit, exponens, psaltis se et geometris multa dicit dedisse.
unde etiam ille mos, ut in conviviis post cenam circumferretur lyra; cuius cum se imperitum Themistocles confessus esset ut verbis Ciceronis utar, est habitus indoctior.