Suetonius, Gaius Caligula 53
“Of the liberal arts, Caligula paid the least attention to literature and the most to rhetoric. He was as eloquent and witty as you would want, especially when he could launch an attack on someone. Words and phrases used to find him whenever he was angry—his articulation and voice too rose up so that it was impossible for him to stay in the same place thanks to excitement and he was heard well by people standing far away.
When he was about to give a speech, he used to threaten to unsheathe the tool of his nocturnal strains, and he despised work composed smoothly and with style so much that he used to say that Seneca wrote “only school-essays” and was “sand without lime”. He was also in the custom of responding to the successful speeches of orators and of working on accusations and defenses for major matters brought to the senate; when his stylus progressed well, whether he was adding guilt or lightening responsibility with his own oration, the whole equestrian class was invited to hear him by edict.”
LIII. Ex disciplinis liberalibus minimum eruditioni, eloquentiae plurimum attendit, quamtumvis facundus et promptus, utique si perorandum in aliquem esset. Irato et verba et sententiae suppetebant, pronuntiatio quoque et vox, ut neque eodem loci prae ardore consisteret et exaudiretur a procul stantibus. Peroraturus stricturum se lucubrationis suae telum minabatur, lenius comptiusque scribendi genus adeo contemnens, ut Senecam tum maxime placentem “commissiones meras” componere et “harenam esse sine calce” diceret. Solebat etiam prosperis oratorum actionibus rescribere et magnorum in senatu reorum accusationes defensionesque meditari ac, prout stilus cesserat, vel onerare sententia sua quemque vel sublevare, equestri quoque ordine ad audiendum invitato per edicta.