As far as the Bible, as a book now, all I have to say about that is that it has been rewritten and translated and copied and edited so many times that well, it's hard to know what's been put in or taken out for political reasons and what is genuine. That of course is AS A BOOK, I'm not saying a word about religion.
This was actually the reason King James sent scholars to the Holy Land to create the "King James Version", which was tranlated directly from the oldest known copies of the Bible books. This is not to say that it is definitive, but it is the best that could be done with the information available. Catholic scholars have done likewise with at least two translations direct from the originals.
The King James scholars rejected fourteen books of the old testament as 'not canonical', either because they considered the translations suspect or they did not consider them 'divinely inspired'. They are called "Apocryphal" books by protestant. Eleven of these are retained in the Catholic and Orthodox Bibles, where they are referred to as 'deuterocanonical' books.
As far as the Roman historians, I've not read but a little of Livy. I've read accounts by Tacitus, which seem to be pretty much a matter-of-fact record of events. Ceaser's accounts of his conquests are no doubt embellished, but they, historically speaking, the best available. I would ask, does the inclusion of Romulus and Remus in historical accounts by Rmans differ greatly than including such phrases as "to the greater glory of God" or "by the Hand of God" in Christian histories? Roman theology differed from ours, and I do not pretend to know how devoutly the various Romans who wrote history believed in it. I would expect that, like publishing in the Christian dominated lands or in Arab lands, in order to be accepted for publication, the writings may have required such entries to pass the censors.
The Ceasers and the Senate maintained records of their proceedings. I will note that, even today, Congressmen and Senators have the authority to embellish, extend, and revise their remarks as recorded in the Congressional Record. The Constitution requires them to maintain an account of their proceedings, but it does not require a verbatim account. Many take advantage of this to make themselves appear more statesmanlike on paper than they do on the floor.
I said the Romans liked to write histories, I didn't say they liked to write accurate histories. Nor do I believe that many of the histories written today are considerably more accurate. One flawed history book will be used as a reference for many later ones. I can cite numerous accounts of World War II events that are being rewritten today, sometimes accurately, sometimes not. In some cases, accurate histories are now being published as witnesses who would not report events in the past out of respect for those whose images may have been tarnished by accurate accounts, come forward to bare their souls before they pass on. Others are rewritten with a view towards the politics of the day.
History is like that. No one can write a definitive history of the events that led to the War in Iraq except those who made the decisions, yet many will try. On the other hand, if the methods used to lead us to war were not 'pure', those who are qualified to write a history of the events will not write them in manner that will show them in a negative light. When all is said and done, and the history is written, it will reflect the views and biases of the writer and of the sources the writer relied on for his 'facts'.