The Bible was written by eyewitnesses
Some apologists claim that the Bible was written by eyewitnesses.
- "The Bible was written by people who witnessed the events it describes "
There are many good reasons to reject this argument, such as the sheer impracticality, inconsistencies, factual errors, commonality of text and style in the gospels, etc. Even if they were to be taken as eye witness accounts, it is dangerous to take them at face value. The writers may be witnesses but have filtered or manipulated their account to fit their agenda (such as increasing faith in their new religion). The writers of the Bible cannot simply be assumed to be trustworthy.
Arguments that the Bible was written by eye witnesses
It is traditionally thought that the Bible was written by people directly involved in the events, such as Moses, Solomon, Apostles or close associates of Jesus. However, there is no evidence to support this claim. The names of the gospels are not the names of the authors, who are in fact anonymous.
Biblical claims of being an eye witness
"So Moses wrote this law and delivered it to the priests, the sons of Levi, who bore the ark of the covenant of the Lord, and to all the elders of Israel"
- "The writer of the gospel of John was obviously an eyewitness of the events of Christ's life since he speaks from a perspective of having been there during many of the events of Jesus' ministry "
- "John’s gospel, for instance, claims to be written by someone who is actually at the last Supper and an immediate disciple of Jesus (John 21:24 ). And the historical evidence for John as this person is very strong (the link between Irenaeus and Polycarp bears this out). Another example that the Gospels contain “eyewitness” testimony comes from the Gospel of Mark. We have early, widespread, and uniform patristic testimony that this Gospel was written by Mark the disciple of Peter, and that the Gospel therefore contains Peter’s eyewitness accounts."
The gospel of John was written many decades after the events, making an eye witness author unlikely, and a mere claim to be an eye witness in the text is not enough to establish it.
Using the Bible to show it was written by eye witnesses leads to a circular argument because it assumes the Bible is true and the existence of eye witnesses are only relevant in establishing the truth of the Bible.
Another example: it is claimed that II Peter 1:16 shows that the New Testament was written by eyewitnesses. However, the books of the New Testament were originally circulated independent of one another, so even if II Peter were written by an eyewitness to Jesus' ministry, it would have no bearing on the authorship of the gospels. Furthermore, a close comparison of II Peter to the epistle of Jude shows that the author of II Peter plagarized Jude, and for this reason, among others, scholars have almost unanimously concluded that II Peter is not authentic.
Most chapters of the Bible do not claim to be eye witness testimony.
- "But nowhere in the Bible is it specifically stated that Moses wrote the entire Pentateuch. "
Moses was only alive for a small part of the Pentateuch, so the belief that he wrote it is incompatible with the notion it was written by eye witnesses.
No eye witnesses could have seen the start of creation, so parts of Genesis could not have been written by eye witnesses
There is a significant amount of reuse of text in the gospels, implying a pre-existing oral history or a complex chain of authors and editors. Eye witness testimony would be expected to be largely unique with a significantly different emphasis in each. The gospels are too similar in the phrases and content to be independent eye witness testimony.
- "Why would an eyewitness like Matthew need to use ninety percent of somebody else's book? "
Many sections of the Bible occur where no witnesses were even possible! For instance, who can say what Jesus prayed in the Garden of Gethsemane, since Jesus was alone and his disciples were asleep? Matthew 26:39 This alone rules out the possibility of the gospels being eye witness accounts.
There is a lack of understanding of Jewish culture by the author of the Gospel of Mark, showing he could not have been an eye witness. The same errors were repeated in the Gospel of Luke. These errors were revised by the author of the Gospel of Matthew This is significant because the Gospel of Mark was probably the first written and if this was not eye witness testimony, the later gospels using Mark as a basis probably were not eye witness testimony either.
- "The Gospels are dated traditionally as follows: Mark is believed to be the first gospel written around A.D. 60. Matthew and Luke follow and are written between A.D. 60-70; John is the final gospel, written between A.D. 90-100. "
It is unlikely many people would have survived from the time of Jesus to the time the gospels, particularly the later ones, were written.  Estimating life expectancy for the disciples of Jesus is complicated by the high infant mortality rate. According to an analysis of Roman census data, a person surviving to 20 years of age could expect to live to 48 years old on average, and a 30 year old could expect to live to about 53.  However, this is only an approximation because local conditions and social class make a large difference to life expectancy. If the disciples of Jesus were (optimistically) 20-30 years of age at his death (assumed 33 CE), they would die on average 56 CE to 61 CE. Life expectancy may be significantly less if the early Christians were persecuted. Perhaps slightly more than half of the eye witness disciples would be dead by the time the first gospel was written, and perhaps none (or very few) would be alive at the time of authorship of the last gospel.
Eye witness testimony is usually written soon after the events they describe. The gospels are not written soon after the events they describe. The many decades between the events and the record would lead to significant errors, mistakes and omissions.
For the author to be an eye witness to the entire story of the gospel, they would have to have followed Jesus almost constantly for their entire life. This is simply not credible because of its impracticality. A witness could not have followed Jesus that closely, to be at the nativity, to be in Egypt, his stay in the wilderness, his mission in Galilee, at the transfiguration, at Gethsemane, at his trial, present at the meeting of Jesus and Pontius Pilate, at the crucifixion and at the empty tomb! Such a person would have been recognised as a follower of Jesus and arrested.
Even many Christian apologists argue that the gospels were not eyewitness accounts. 
The Epistles of Peter claim to be written by the apostle Peter, an eye witness to the life of Jesus. 1 Peter 5:1 However, Biblical scholarship now consider these letters to have been falsely attributed to him. This means these epistles are lying when they claim to be authored by an eye witness.
The Bible contains errors and inconsistencies. Of course, eye witness testimony often contains mistakes. However, many errors are simply lack of knowledge or fanciful story telling, such as Jacob's tribe in Egypt and Moses leading them to the promised land (which didn't happen).
The resurrection had eyewitnesses
A closely related claim is that the resurrection of Jesus had eyewitnesses:
- "The empty tomb may be the strongest proof Jesus Christ rose from the dead." 
- "The holy women eyewitnesses are further proof that the Gospels are accurate historical records." "The first eyewitnesses of the resurrection were women."
- "A large crowd of more than 500 eyewitnesses saw the risen Jesus Christ at the same time." 1 Corinthians 15:6 
- various other sightings and visions that are recorded in the New Testament.
These claims suffer from the same problem: the New Testament was not written by eyewitnesses. We are relying on anonymous authors who claim there were eyewitnesses. Even if there were witnesses of the resurrection, we do not reliably know they existed.
- The Bible is not a reliable historical source
- Many accurate copies of my holy book exist
- Embarrassing testimony
- Did Jesus Even Exist? Responding to 5 Objections Raised by @rawstory, December 17, 2015
- Evid3nc3, Atheism - A History of God (The Polytheistic Origins of Christianity and Judaism)
- David Fitzgerald, 
-  Adapted from "Frier's Life Table for the Roman Empire," p.144 of T.G. Parkin, Demography and Roman Society (1992)