However, to convince readers of his superiority Guibert knew that stylistic competence was necessary but not sufficient, particularly because both Fulker and the author of the Gesta Francorum had convinced most readers, including Guibert himself, that they were eye-witnesses of most of the events in their texts.[25] Guibert then had to deal with the commonplace assumption passed on by Isidore of Seville: Apud veteres enim nemo conscribebat historiam, nisi is qui interfuisset, et ea quae conscribend essent vidisset.[26] Among the ancients no one wrote history unless he had been present and had seen the things he was writing about. To overcome his apparent disadvantage, Guibert offers defense of his second-hand perspective several times in the course of his performance. In the fifth book, immediately after acknowledging the fascination of what is difficult, Guibert provides two paragraphs on the difficulties of determining exactly what happened at Antioch. These paragraphs offer another opportunity to watch Guibert rework material from an earlier text. The author of the Gesta Francorum had invoked variation of the topos of humility,[27] just before giving his account of how Antioch was betrayed by someone inside the city: I am unable to narrate everything that we did before the city was captured, because no one who was in these parts, neither cleric nor laity, could write or narrate entirely what happened. But I shall tell a little.[28] When Guibert takes his turn at the topos, he is clearly determined to outdo the author of the Gesta Francorum, both stylistically and in terms of the theory of historiography: We judge that what happened at the siege of Antioch cannot possibly be told by anyone, because, among those who were there, no one can be found who could have observed everything that took place throughout the city, or who could understand the entire event in a way that would enable him to represent the sequence of actions as they took place. At the beginning of the fourth book of the Gest Dei, Guibert's defense of his absence is again intertextual, but openly polemic as well, as he declares the battle between modern Christian writing (saints lives and John III.32) and ancient pagan authority (Horace, Ars Poetica 180-181) no contest: If anyone objects that I did not see, he cannot object on the grounds that I did not hear, because I believe that, in a way, hearing is almost as good as seeing. For although: Less vividly is the mind stirred by what finds entrance through the ears than by what is brought before the trusty eyes.[29] Yet who is unaware that historians and those who wrote the lives of the saints wrote down not only what they had seen, but also those things they had drawn from what others had told them? If the truthful man, as it is written, reports "what he has seen and heard," then his tale may be accepted as true when he describes what he has not seen, but has been told by reliable speakers.