Procopius 
The Secret History of the Court of Justinian [EPUB ebook] 

I have thus described the fortunes of the Romans in their wars up to the present day, as far as possible assigning the description of events to their proper times and places. What follows will not be arranged with the same exactness, but everything shall be written down as it took place throughout the whole extent of the Roman empire. My reason for this is, that it would not have been expedient for me to describe these events fully while those who were their authors were still alive; for, had I done so, I could neither have escaped the notice of the multitude of spies, nor, had I been detected, could I have avoided a most horrible death; for I could not even have relied upon my nearest relatives with confidence. Indeed, I have been forced to conceal the real causes of many of the events recounted in my former books. It will now be my duty, in this part of my history, to tell what has hitherto remained untold, and to state the real motives and origin of the actions which I have already recounted. But, when undertaking this new task, how painful and hard will it be, to be obliged to falter and contradict myself as to what I have said about the lives of Justinian and Theodora: and particularly so, when I reflect that what I am about to write will not appear to future generations either credible or probable, especially when a long lapse of years shall have made them old stories; for which reason I fear that I may be looked upon as a romancer, and reckoned among playwrights. However, I shall have the courage not to shrink from this important work, because my story will not lack witnesses; for the men of to-day, who are the best informed witnesses of these facts, will hand on trustworthy testimony of their truth to posterity. Yet, when I was about to undertake this work, another objection often presented itself to my mind, and for a long time held me in suspense.
I doubted whether it would be right to hand down these events to posterity; for the wickedest actions had better remain unknown to future times than come to the ears of tyrants, and be imitated by them. For most rulers are easily led by lack of knowledge into imitating the evil deeds of their predecessors, and find it their easiest plan to walk in the evil ways of their forefathers.
Later, however, I was urged to record these matters, by the reflection that those who hereafter may wish to play the tyrant will clearly see, in the first place, that it is probable that retribution will fall upon them for the evil that they may do, seeing that this was what befell these people; and, secondly, that their actions and habits of life will be published abroad for all time, and therefore they will perhaps be less ready to transgress. Who, among posterity, would have known of the licentious life of Semiramis, or of the madness of Sardanapalus or Nero, if no memorials of them had been left to us by contemporary writers? The description of such things, too, will not be entirely without value to such as hereafter may be so treated by tyrants; for unhappy people are wont to console themselves by the thought that they are not the only persons who have so suffered. For these reasons, I shall first give a description of the evil wrought by Belisarius, and afterwards I shall describe the misdeeds of Justinian and Theodora…