It's not just the bible.
Jesus was mentioned by other historical contemporaries, particularly Josephus, Tacitus, and Suetonius. Of them all, Josephus is the most detailed and, it must be noted, he was not a Christian:
At this time there was a wise man who was called Jesus. And his conduct was good, and (he) was known to be virtuous. and many people from among the Jews and the other nations became his disciples. Pilate condemned him to be crucified and to die. And those who had become his disciples did not desert his discipleship. They reported that he had appeared to them three days after his crucifixion and that he was alive; accordingly, he was perhaps the Messiah concerning whom the prophets have recounted wonders.
Tacitus mentions Jesus in relation to Pilate who, after the crucifixion, was recalled to Rome for his mismanagement of Judea, the complaints of which included mass executions for minor offenses or even no offense at all (as Jesus supposedly was):
Nero fastened the guilt [of starting the blaze] and inflicted the most exquisite tortures 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 [14-37] at the hands of one of our procurators, 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, where all things hideous and shameful from every part of the world find their centre and become popular.
Other sources include Lucian, Thallus, and Celsus.
Jesus as well as can be documented from such a far time, almost certainly existed.
Whether he died on the cross is not documented outside of the bible save Josephus' statement. The Talmud says he was hanged. Given Pilate's excesses in the use of crucifixion however, it is likely that this is how he died.
"The darkness which descended upon the land," at the time of Jesus' death was also independently documented.
