Aulus Gellius, Attic Nights 9.9:
When remarkable expressions are to be translated or imitated from the Greek, we must not strive to turn all of the words entirely into the mode in which they have been expressed. They quite often lose their grace if they are translated as if against their will or refusing the process. Vergil, therefore, acted knowingly and shrewdly when, working up some passages of Homer or Apollonius or Parthenius or Callimachus or Theocritus or some other poets, he abandoned some part of the work and expressing another. Thus, quite recently at table when the bucolic poems of both Theocritus and Vergil were being read at the same time, we noticed that Vergil abandoned some of the expressions which, although they were marvelously charming in the Greek, neither should nor could have been translated into Latin.
Quando ex poematis Graecis vertendae imitandaeque sunt insignes sententiae, non semper aiunt enitendum, ut omnia omnino verba in eum, in quem dicta sunt, modum vertamus. Perdunt enim gratiam pleraque, si quasi invita et recusantia violentius transferantur. Scite ergo et considerate Vergilius, cum aut Homeri aut Hesiodi aut Apollonii aut Parthenii aut Callimachi aut Theocriti aut quorundam aliorum locos effingeret, partem reliquit, alia expressit. Sicuti nuperrime aput mensam cum legerentur utraque simul Bucolica Theocriti et Vergilii, animadvertimus reliquisse Vergilium, quod Graecum quidem mire quam suave est, verti autem neque debuit neque potuit.