“Although there is overwhelming evidence that the New Testament is an accurate and trustworthy historical document, many people are still reluctant to believe what it says unless there is also some independent, non-biblical testimony that corroborates its statements,” writes Dr. Michael Gleghorn.
Here Dr. Gleghorn examines evidence from ancient non-Christian sources for the life of Jesus (see original article for bibliographical notes) — sources largely complied in F.F. Bruce’s 1974 book Jesus and Christian Origins Outside the New Testament — which help confirm the historical reliability of the Gospels:
Evidence from Tacitus
….In the introduction to one of his books, F.F. Bruce tells about a Christian correspondent who was told by an agnostic friend that “apart from obscure references in Josephus and the like,” there was no historical evidence for the life of Jesus outside the Bible.  This, he wrote to Bruce, had caused him “great concern and some little upset in [his] spiritual life.”  He concludes his letter by asking, “Is such collateral proof available, and if not, are there reasons for the lack of it?” The answer to this question is, “Yes, such collateral proof is available,” and we will be looking at some of it in this article.
Let’s begin our inquiry with a passage that historian Edwin Yamauchi calls “probably the most important reference to Jesus outside the New Testament.”  Reporting on Emperor Nero’s decision to blame the Christians for the fire that had destroyed Rome in A.D. 64, the Roman historian Tacitus wrote:
“Nero fastened the guilt….on a class hated for their abominations, called Christians by the populace. Christus, from whom the name had its origin, suffered the extreme penalty during the reign of Tiberius at the hands of….Pontius Pilatus, and a most mischievous superstition, thus checked for the moment, again broke out not only in Judaea, the first source of the evil, but even in Rome….” 
What all can we learn from this ancient (and rather unsympathetic) reference to Jesus and the early Christians? Notice, first, that Tacitus reports Christians derived their name from a historical person called Christus (from the Latin), or Christ. He is said to have “suffered the extreme penalty,” obviously alluding to the Roman method of execution known as crucifixion. This is said to have occurred during the reign of Tiberius and by the sentence of Pontius Pilatus. This confirms much of what the Gospels tell us about the death of Jesus.
But what are we to make of Tacitus’ rather enigmatic statement that Christ’s death briefly checked “a most mischievous superstition,” which subsequently arose not only in Judaea, but also in Rome? One historian suggests that Tacitus is here “bearing indirect . . . testimony to the conviction of the early church that the Christ who had been crucified had risen from the grave.”  While this interpretation is admittedly speculative, it does help explain the otherwise bizarre occurrence of a rapidly growing religion based on the worship of a man who had been crucified as a criminal.  How else might one explain that?
Evidence from Pliny the Younger
Another important source of evidence about Jesus and early Christianity can be found in the letters of Pliny the Younger to Emperor Trajan. Pliny was the Roman governor of Bithynia in Asia Minor. In one of his letters, dated around A.D. 112, he asks Trajan’s advice about the appropriate way to conduct legal proceedings against those accused of being Christians.  Pliny says that he needed to consult the emperor about this issue because a great multitude of every age, class, and sex stood accused of Christianity.
At one point in his letter, Pliny relates some of the information he has learned about these Christians:
“They were in the habit of meeting on a certain fixed day before it was light, when they sang in alternate verses a hymn to Christ, as to a god, and bound themselves by a solemn oath, not to any wicked deeds, but never to commit any fraud, theft or adultery, never to falsify their word, nor deny a trust when they should be called upon to deliver it up; after which it was their custom to separate, and then reassemble to partake of food — but food of an ordinary and innocent kind.” 
This passage provides us with a number of interesting insights into the beliefs and practices of early Christians. First, we see that Christians regularly met on a certain fixed day for worship. Second, their worship was directed to Christ, demonstrating that they firmly believed in His divinity. Furthermore, one scholar interprets Pliny’s statement that hymns were sung to Christ, as to a god, as a reference to the rather distinctive fact that, “unlike other gods who were worshipped, Christ was a person who had lived on earth.”  If this interpretation is correct, Pliny understood that Christians were worshipping an actual historical person as God! Of course, this agrees perfectly with the New Testament doctrine that Jesus was both God and man.
Not only does Pliny’s letter help us understand what early Christians believed about Jesus’ person, it also reveals the high esteem to which they held His teachings. For instance, Pliny notes that Christians bound themselves by a solemn oath not to violate various moral standards, which find their source in the ethical teachings of Jesus. In addition, Pliny’s reference to the Christian custom of sharing a common meal likely alludes to their observance of communion and the “love feast.”  This interpretation helps explain the Christian claim that the meal was merely food of an ordinary and innocent kind. They were attempting to counter the charge, sometimes made by non-Christians, of practicing “ritual cannibalism.”  The Christians of that day humbly repudiated such slanderous attacks on Jesus’ teachings. We must sometimes do the same today.
Evidence from Josephus
Perhaps the most remarkable reference to Jesus outside the Bible can be found in the writings of Josephus, a first century [Judean] historian. On two occasions, in his Jewish Antiquities, he mentions Jesus. The second, less revealing, reference describes the condemnation of one “James” by the Jewish Sanhedrin. This James, says Josephus, was “the brother of Jesus the so-called Christ.”  F.F. Bruce points out how this agrees with Paul’s description of James in Galatians 1:19 as “the Lord’s brother.”  And Edwin Yamauchi informs us that “few scholars have questioned” that Josephus actually penned this passage. 
[Editor’s Note: In Book 20, Chapter 9 of Josephus’ “Antiquities of the Jews,” there is a reference to “the brother of Jesus, who was called Christ, whose name was James,” and that this James was put to death by stoning. Many Christians cite this reference as more historical proof of Jesus Christ, but the problem is that clearly this passage is referring to a different Jesus — “the son of Damneus, high priest,” according to Josephus. Of course, Josephus could have misidentified the father of Jesus here as Damneus, but we can only conjecture about it.]
As interesting as this brief reference is, there is an earlier one, which is truly astonishing. Called the “Testimonium Flavianum,” the relevant portion declares:
“About this time there lived Jesus, a wise man, if indeed one ought to call him a man. For he….wrought surprising feats….He was the Christ. When Pilate….condemned him to be crucified, those who had….come to love him did not give up their affection for him. On the third day he appeared….restored to life….And the tribe of Christians….has….no disappeared.” 
Did Josephus really write this? Most scholars think the core of the passage originated with Josephus, but that it was later altered by a Christian editor, possibly between the third and fourth century A.D.  But why do they think it was altered? Josephus was not a Christian, and it is difficult to believe that anyone but a Christian would have made some of these statements.
For instance, the claim that Jesus was a wise man seems authentic, but the qualifying phrase, “if indeed one ought to call him a man,” is suspect. It implies that Jesus was more than human, and it is quite unlikely that Josephus would have said that. It is also difficult to believe he would have flatly asserted that Jesus was the Christ, especially when he later refers to Jesus as “the so-called” Christ. Finally, the claim that on the third day Jesus appeared to His disciples restored to life, inasmuch as it affirms Jesus’ resurrection, is quite unlikely to come from a non-Christian.
But even if we disregard the questionable parts of this passage, we are still left with a good deal of corroborating information about the biblical Jesus. We read that he was a wise man who performed surprising feats. And although He was crucified under Pilate, His followers continued their discipleship and became known as Christians. When we combine these statements with Josephus’ later reference to Jesus as “the so-called Christ,” a rather detailed picture emerges which harmonizes quite well with the biblical record. It increasingly appears that the “biblical Jesus” and the “historical Jesus” are one and the same.
Evidence from Lucian
Lucian of Samosata was a second century Greek satirist. In one of his works, he wrote of the early Christians as follows:
“The Christians . . . worship a man to this day–the distinguished personage who introduced their novel rites, and was crucified on that account. . . . [It] was impressed on them by their original lawgiver that they are all brothers, from the moment that they are converted, and deny the gods of Greece, and worship the crucified sage, and live after his laws.” 
Although Lucian is jesting here at the early Christians, he does make some significant comments about their founder. For instance, he says the Christians worshipped a man, “who introduced their novel rites.” And though this man’s followers clearly thought quite highly of Him, He so angered many of His contemporaries with His teaching that He “was crucified on that account.”
Although Lucian does not mention his name, he is clearly referring to Jesus. But what did Jesus teach to arouse such wrath? According to Lucian, he taught that all men are brothers from the moment of their conversion. That’s harmless enough. But what did this conversion involve? It involved denying the Greek gods, worshipping Jesus, and living according to His teachings. It’s not too difficult to imagine someone being killed for teaching that. Though Lucian doesn’t say so explicitly, the Christian denial of other gods combined with their worship of Jesus implies the belief that Jesus was more than human. Since they denied other gods in order to worship Him, they apparently thought Jesus a greater God than any that Greece had to offer.