Aulus Gellius, Noctes Atticarum  10.1.1-9 (ca. A.D. 180): ‘Tertiam'ne consul an ‘tertio' dici oporteat; et quonam modo Cn. Pompeius, cum in theatro, quod erat dedicaturus, honores suos inscriberet, quaestionem ancipitem istius verbi de consilio Ciceronis vitaverit.  1. Familiari meo cuipiam litteras Athenis Romam misi. 2. In his scriptum fuit me illi tam ‘tertium' scripsisse. 3. Is ad me rescripsit petiuitque, ut rationem dicerem, cur ‘tertiam' ac non ‘tertio' scripsissem. Id etiam adscripsit, ut eadem, quid super illo quoque mihi videtur, facerem se certiorem, ‘tertium' ne ‘consul' et ‘quartum' an ‘tertio' et ‘quarto' dicendum esset, quoniam Romae doctum virum dicere audisset ‘tertio' et ‘quarto' consul, non ‘tertium' que; idque in principio libri * * * Coelium scripsisse et Quintum Claudium in libro undevicesimo C. Marium creatum ‘septimo' consulem dixisse. 4. Ad haec ego rescripsi nihil amplius quam verba M. Varronis, hominis, opinor, quam fuit Claudius cum Coelio doctioris, quibus verbis utrumque, de quo ad me scripserat, decideretur; 5. nam et Varro satis aperte, quid dici oporteret, edocuit, et ego adversus eum, qui doctus esse dicebatur, litem meam facere absens nolui. 6. Verba M. Varronis ex libro Disciplinarum quinto haec sunt: "Aliquid est ‘quarto' praetorem fieri et ‘quartum;' quod ‘quarto' locum adsignificat ac tres ante factos, ‘quartum' tempus adsignificat et ter ante factum. Igitur Ennius recte, quod scripsit: Quintus pater quartum fit consul, et Pompeius timide, quod in theatro, ne adscriberet ‘consul tertium' aut ‘tertio,' extremas litteras non scripsit." 7. Quod de Pompeio Varro breviter et subobscure dixit, Tiro Tullius, Ciceronis libertus, in epistula quadam enarratius scripsti ad hunc ferme modum: "Cum Pompeius,' inquit, "aedem Victoriae dedicaturus foret, cuius gradus vicem theatri essent, nomenque eius et honores inscriberentur, quaeri coeptum est utrum ‘consul tertio' inscribendum esset an ‘tertium.' Eam rem Pompeius exquisitissime rettulit ad doctissimos civitatis, cumque dissentiretur et pars ‘tertio,' aliii ‘tertium' scribendum contenderent, rogavit," inquit, "Ciceronem Pompeius, ut quod ei rectius videretur scribi iuberet," Tum Ciceronem iudicare de viris doctis veritum esse, ne, quorum opinionem inprobasset, ipsos videretur inprobasse. "Persausit igitur Pompeio, ut neque ‘tertium' neque ‘tertio' scriberetur, sed ad secundam usque "t" fierent litterae, ut verbo perscripto res quidem demonstraretur, sed dictio tamen ambigua verbi lateret. 8. Id autem, quod et Varro et Tiro dixerunt, in eodem nunc theatro non est ita scriptum. 9. Nam cum multis annis postea scaena, quae prociderat, refecta esset, numerus tertii consulatus non uti initio primoribus litteris, sed tribus tantum liniolis incisis signifactus est. Whether one ought to say tertium consul or tertio; and how Gnaeus Pompeius, when he would inscribe his honors on the theater which he was about to dedicate, by Cicero's advice evaded the difficulty as to the form of that word. 1. I sent a letter from Athens to a friend of mine in Rome. 2. In it I said that I had now written him for the third time (tertium). 3. In his reply he asked me to give my reason for having written tertium and not tertio. He added that he hoped I would at the same time inform him what I thought about the question whether one should say tertium consul, meaning "consul for the third time" and quartum or tertio and quarto; since he had heard a learned man at Rome say tertio and quarto consul, not tertium and quartum; also, that Coelius had so written at the beginning of his third book and that Quintus Claudius in his eleventh book said that Marius was chosen consul for the seventh time, using septimo. 4. In reply to these questions, to decide both matters about which he had written to me, I contented myself with quoting Marcus Varro, a more learned man in my opinion that Coelius and Claudius together. 5. For Varro has made it quite plain what ought to be said, and I did not wish, when at a distance, to enter into a dispute with a man who had the name of being learned. 6. Marcus Varro's words, in the fifth book of his Discliplinae, are as follows: "It is one thing to be made praetor quarto and another quartum; for quarto refers to order and indicates that three were elected before him; quartum refers to time and indicates that he had been made praetor three times before. Accordingly Ennius was right when he wrote: ‘Quintus, his sire, a fourth time (quartum) consul is,' and Pompeius was timid when, in order to avoid writing consul tertiam or tertio on his theater, he did not write the final letters." 7. What Varro briefly and somewhat obscurely hinted at concerning Pompeius, Tullius Tiro, Cicero's freedman, wrote at greater length in one of his letters, substantially as follows: "When Pompeius was preparing to consecrate the temple of Victory, the steps of which formed his theater, and to inscribe upon it his name and honors, the question arose whether consul tertium should be written, or tertio. Pompeius took great pains to refer th question to the most learned men of Rome, and when there was a difference of opinion, some maintaining that tertio ought to be written, others tertium, Pompeius asked Cicero," says Tiro, "to decide upon what seemed to him the most correct form." Then Cicero was reluctant to pass judgment upon learned men, lest he might seem to have censured the men themselves in criticizing their opinion. "He accordingly advised Pompeius to write neither tertium or tertio, but to inscribe the first four letters only, so that the meaning was shown without writing the whole word, but yet the doubt as to the form of the word was concealed." 8. But that of which Varro and Tiro spoke is not now written in that way on this same theater. 9. For when many years later, the back wall of the stage had fallen and was restored, the number of the third consulship was indicated, not as before, by the first four letters, but merely by three incised lines. (J. C. Rolfe, trans.)