I wrote on this topic about a month ago, here and here but I just wanted to add a few more evidences, outside the Gospels themselves, which add to the credibility of the Gospel accounts.

1. Non-Christian sources
There are 11 ancient references to Jesus in non-Christian sources. This is actually quite surprising because Galilee and even Jerusalem were not important places at that time. So the fact that a Jewish carpenter who was not rich or famous would rate a mention in the histories of that time is significant. The most important of these references, from an apologetic point of view are: Tacitus who wrote imperial Roman history in about AD 100 and Josephus who was a Jewish historian at about the same time. These writings along with the other nine, confirm that there was a famous Jewish teacher and healer who was executed by the Romans. For this reason professional ancient historians do not doubt that Jesus lived.

2. Archaeology
Many archaeological finds have confirmed details that are in the Gospels. For example in 2004 some ancient steps in the Salome area of Jerusalem were discovered. A subsequent archaeological dig found the largest Jewish bathing pool that had ever been discovered. It is believed that this is the Pool of Salome mentioned in John 9.

Archaeological digs can also be important for what they do not find. In Galilee no pig bones have ever been discovered confirming that this area was very Jewish. This is significant because some historians had previously believed that Galilee wasn’t particularly Jewish as there had been discoveries confirming Rome and Greek architecture. However the non-discovery of pig bones plus a large number of Jewish purification bowls confirmed that Galilee was indeed Jewish. Archaeology confirms that the Gospels show a first century Jewish culture.

3. Encyclopaedia Britannica
It is significant that even the Encyclopaedia Britannica, as historian John Dickson discovered, has high regard for the reliability of the New Testament: “Compared with other ancient manuscripts, the test of the New Testament is dependable and consistent” (From John Dickson’s, If I were God I’d make myself clearer, 2002).