Pliny the Younger, Letters 9.1–3; 8-11
“You ask me what I think you should study while you enjoy your current vacation? It is really useful—as many propose—to translate Greek into Latin or Latin into Greek. By this kind of exercise you gain the proper and decorative use of words, an abundance of rhetorical devices, a forceful manner of explication, and, importantly, an ability to compose similar works due to the imitation of the best models. The things which escape a reader, moreover, do not evade a translator. From this practice one acquires intelligence and critical judgment.
From time to time, I want you to pick some passage from a history or perhaps write a letter more carefully. For sometimes even in speech the situation requires not only a bit of historical but even poetic description—a pure and compact style can be found in letters. It is also right to take a break for poetry—I am not talking about a long, continuous poem, since that cannot be completed without a lot of time—but in that sharp and brief style which aptly breaks up your cares and duties however important they are. This is called playing with verse, but these games often attract no less glory than serious pursuits.”
Quaerisquemadmodum in secessu, quo iam diu frueris, putem te studere oportere. Utile in primis, et multi praecipiunt, vel ex Graeco in Latinum vel ex Latino vertere in Graecum. Quo genere exercitationis, proprietas splendorque verborum, copia figurarum, vis explicandi, praeterea imitatione optimorum similia inveniendi facultas paratur; simul quae legentem fefellissent, transferentem fugere non possunt. Intellegentia ex hoc et indicium adquiritur.
Volo interdum aliquem ex historia locum adprendas, volo epistulam diligentius scribas. Nam saepe in oratione quoque non historica modo sed prope poetica descriptionum necessitas incidit, et pressus sermo purusque ex epistulis petitur. Fas est et carmine remitti, non dico continuo et longo (id enim perfici nisi in otio non potest), sed hoc arguto et brevi, quod apte quantas libet occupationes curasque distinguit. Lusus vocantur; sed hi lusus non minorem interdum gloriam quam seria consequuntur.