Historicity
The details of Livy's History of Rome vary from mythical or legendary stories at the beginning to detailed and authentic accounts of apparently real events toward the end. He himself noted the difficulty of finding information about events some 700 years or more removed from the author. Of his material on early Rome he said "The traditions of what happened prior to the foundation of the City or whilst it was being built, are more fitted to adorn the creations of the poet than the authentic records of the historian."
Nevertheless, according to the tradition of writing history at the time, he felt obliged to relate what he read (or heard) without passing judgement as to its truth or untruth. One of the problems of modern scholarship is to ascertain where in the work the line is to be drawn between legendary and non-legendary events. The traditional modern view is that buildings, inscriptions, monuments and libraries prior to the sack of Rome in 387 BCE by the Gauls under Brennus were destroyed by that sack and made unavailable to Livy and his sources. His credible history therefore must begin with that date. A layer of ash over the lowest pavement of the comitium believed to date from that time seemed to confirm a city-wide destruction.
A new view by Tim Cornell, however, deemphasizes the damage caused by the Gauls under Brennus. Among other reasons, he asserts that the Gauls' interest in movable plunder, rather than destruction, kept damage to a minimum. The burnt layer under the comitium is now dated to the 6th century BC. There apparently is no archaeological evidence of a widespread destruction of Rome by the Gauls. Cornell uses this information to affirm the historicity of Livy's 4th- and 5th-century-BCE events.
Read more about this topic: Ab Urbe Condita (book)