When examining historical accounts, one must ask if the witness has an interest in how posterity will view both "the historical record" and him/herself; one must ask what was the proximity of the witness was to the persons/events in question; one must ask what the ability of the witness in question was to comprehend the persons/events in question; finally, one must also take care to make as dispassionate a decision as possible about the source of the witness's information--did s/he physically witness the person/events, or obtain the information at second hand, or read contemporary accounts? These questions often become "nested" on the basis of this last criterion, unless the individual concerned claims to have been an eye-witness, in which case, one is usually only concerned with the first criterion.
Therefore, we can take Eusebius as an example. Eusebius was agressively christian, and sought to promote this belief as the one, true religion. This is self-evident in his writings. He could not claim to have known this particular Joshua of Nazareth, so he relies upon a contention that he has read confirmation of that person's existence, AS the messiah, in the history prepared by Josephus. The first criterion is covered in a description of Eusebius as an historian--he had an interest in promoting the religion which he professed. This makes him a suspect witness. His writing is somewhat vainglorious, in that he touts his own piety--this may or may not make him suspect as a witness, but on the whole, it is another note of caution in accepting what he has written. By citing Josephus, these questions are transferred to him as a source. It is rather clever of Eusebius to have used Josephus as his authority (more on that later). On the first issue, Josephus--never claiming to be and never claimed to have been either a christian, nor an enemy of christianity (not a force of any description in his lifetime, and therefore no threat, either politically or religiously)--qualifies as a disinterested witness, for as much as anyone can ever be. Josephus was writing a history of the Jews to take that record up to the time of the destruction of the Temple, and for a short period thereafter. So, with regards to the second question, Josephus had a reasonal proximity to the person and the events in question. Josephus was in Palestine at the time that Titus destroyed the Jewish rebels, and therefore was personally reasonably reliable as source of information. In short, Josephus would be a reliable canditate for a witness on this topic--if we can accept that he did indeed write what Eusebius claims that he wrote. And now we have reached the crux of the biscuit.
Eusebius is already doubtful on the first issue of his disinterestedness--he is obviously NOT disinterested. On the second issue, he has some credibility as having lived within a few centuries of the probable date of the production of Josephus' text, although it is worth noting at this point that no other source contemporary to either Josephus or Eusebius takes note of any contention on the part of Josephus that this Joshua of Nazareth did in fact exist, AND was the messiah; furthermore, no such fragment of Josephus has since been discovered. I would not question the ability of Eusebius to comprehend what Josephus wrote, for whatever other faults--largely partisan--he has as an historian. Since the source of Eusebius' contention is Josephus, this is precisely the "nested" variety of historigraphic analysis to which i referred earlier. When Constantine made christianity the state religion of the Roman Empire, he did so at the urging of his wife and his mother-in-law (
)--he did not do so to the exclusion of other religious practices in the empire, the Romans were noteworthy for their religious tolerance. He also promulgated his new policy after literally decades of nagging by his wife and mother-in-law, and Eusebius is the only source for the contention that Constantine was himself a christian, AND Eusebius is contradicted on this point by other historians contemporary to the event--more reason to doubt Eusebius.
I've gone on too long here as it is, and may need to clarify what i've written later--but i would like to state, for this forum's record, that i have no good reason to believe that Joshua of Nazareth the Messiah ever existed. I also have no good reason to deny that such an individual existed. I have very good reason not to rely on Eusebius as an historical witness, and i have read Tacitus exhaustively--nowhere in
The History of Imperial Rome nor in
The Annals of Imperial Rome does Tacitus assert that Joshuah of Nazareth the Messiah ever existed, he simply notes the existence of a cult based upon the alleged teachings of such an individual. This hasn't prevented christians from asserting that Tacitus is a source for the existence of this Joshua. Steven has written: "One has to make a distinction between the spiritual reality and the historical record." Very adroitly put, he has gone directly to the heart of this issue. The historical record is, in fact, mute on this subject, with the single exception of the thoroughly suspect testimony of Eusebius. You have mentioned Emperors and Monarchs--i think it not unfair to say that such a contention ought to be supported with verifiable citations. I know of no such information coming from Octavian (Augustus), Tiberius, Gaius (Caligula), Claudius or Brittanicus (Nero)--the only emperors who meet the criterion for proximity, either in time or space. I do not wish to have what i write accepted as a statement from authority--i have read and re-read Roman history and literature for 45 years, since, as a child, i first began a life-long obsession. I would only concede such a point on the basis of a reliably verifiable citation--so, i do not deny, nor do i accept the contention of the existence of Joshua the Messiah. Steve's point about spiritual reality is important, in that much may be explained on this basis, without reference to historigraphically sound sources. It matters not, really, whether such an individual ever existed. What matters most, is that some believe and have believed that to be the case, and based upon the religious flavor-of-the-month, have acted accordingly. None of what i write here is meant to belittle you, or the beliefs that you hold. As a life-long, convinced and dedicated Irish-American, raised by immigrant grandparents, i also lay claim to an inherent and facetious irreverance on just about any subject--so i hope that you will understand that i entertained myself in this thread for entertainment's sake alone, and not as a slur against you, nor a condemnation of beliefs anyone sincerely holds. I would like to state for this forum's record that i trust religious leaders about as far as i can throw a bull moose.