Antiquities of the Jews by Flavius Josephus

Those who undertake to write histories, do not, I perceive, take that trouble on one and the same account, but for many reasons, and those such as are very different one from another. For some of them apply themselves to this part of learning to show their skill in composition, and that they may therein acquire a reputation for speaking finely: others of them there are, who write histories in order to gratify those that happen to be concerned in them, and on that account have spared no pains, but rather gone beyond their own abilities in the performance: but others there are, who, of necessity and by force, are driven to write history, because they are concerned in the facts, and so cannot excuse themselves from committing them to writing, for the advantage of posterity; nay, there are not a few who are induced to draw their historical facts out of darkness into light, and to produce them for the benefit of the public, on account of the great importance of the facts themselves with which they have been concerned. Now of these several reasons for writing history, I must profess the two last were my own reasons also; for since I was myself interested in that war which we Jews had with the Romans, and knew myself its particular actions, and what conclusion it had, I was forced to give the history of it, because I saw that others perverted the truth of those actions in their writings.