Gene Callahan claims they did not, but his evidence is unconvincing. It is true that historians in the ancient period enjoyed the license to invent speeches. That was an established feature of their genre—and if I get the time, I will blog on a striking example of this. But that is a far cry from lacking the concept of authenticity. In demonstrating that Dr. Callahan is wrong, probably the best place to start is with a lengthy quotation from Thucydides himself (translated, of course, into English):
With reference to the speeches in this history, some were delivered before the war began, others while it was going on; some I heard myself, others I got from various quarters; it was in all cases difficult to carry them word for word in one’s memory, so my habit has been to make the speakers say what was in my opinion demanded of them by the various occasions, of course adhering as closely as possible to the general sense of what they really said. And with reference to the narrative of events, far from permitting myself to derive it from the first source that came to hand, I did not even trust my own impressions, but it rests partly on what I saw myself, partly on what others saw for me, the accuracy of the report being always tried by the most severe and detailed tests possible. My conclusions have cost me some labour from the want of coincidence between accounts of the same occurrences by different eye-witnesses, arising sometimes from imperfect memory, sometimes from undue partiality for one side or the other. The absence of romance in my history will, I fear, detract somewhat from its interest; but if it be judged useful by those inquirers who desire an exact knowledge of the past as an aid to the interpretation of the future, which in the course of human things must resemble if it does not reflect it, I shall be content. In fine, I have written my work, not as an essay which is to win the applause of the moment, but as a possession for all time.
Obviously, then, Thucydides did not think his inclusion of fictitious speeches was justified by some general license to make things up.
Consider, moreover, the following ancient passages—all of which reflect a well-developed concept of historical accuracy:
“And in this wise he was stabbed with three and twenty wounds, uttering not a word, but merely a groan at the first stroke, though some have written that when Marcus Brutus rushed at him, he said in Greek, ‘You too, my child?'” Suet. Jul. 82.2.
“And it is said by some writers that although Caesar defended himself against the rest and darted this way and that and cried aloud, when he saw that Brutus had drawn his dagger, he pulled his toga down over his head and sank, either by chance or because pushed there by his murderers, against the pedestal on which the statue of Pompey stood.” Plut. Caes. 66.12.
“Some have supposed that Tiberius was born at Fundi, on no better evidence than that his maternal grandmother was a native of that place, and that later a statue of Good Fortune was set up there by decree of the senate. But according to the most numerous and trustworthy authorities, he was born at Rome, on the Palatine, the sixteenth day before the Kalends of December, in the consulship of Marcus Aemilius Lepidus and Lucius Munatius Plancus (the former for the second time) while the war of Philippi was going on. In fact it is so recorded both in the calendar and in the public gazette. Yet in spite of this some write that he was born in the preceding year, that of Hirtius and Pansa, and others in the following year, in the consulate of Servilius Isauricus and Lucius Antonius.” Suet. Tib. 5.
“His son, surnamed Sabinus (although some say that he was an ex-centurion of the first grade; others that while still in command of a cohort he was retired because of ill-health) took no part in military life, but farmed the public tax of a fortieth in Asia.” Suet. Ves. 1.2.
“How can it then be other than an absurd thing for the Greeks to be so proud, and to vaunt themselves to be the only people that are acquainted with antiquity, and that have delivered the true accounts of those early times after an accurate manner! Nay, who is there that cannot easily gather from the Greek writers themselves, that they knew but little on any good foundation when they set to write, but rather wrote their histories from their own conjectures!” J. Ap. 1.15.
With evidence like this (and many other examples could be cited), it is simply not plausible to maintain that the ancients did not have the concept of historical accuracy.