According to the gospels, Jesus died less than six hours after he was put on the cross. This was much sooner than normal, because victims of crucifixions usually lived much longer, at least 24 hours, and sometimes several days. Mark 15:44 says that the Roman governor Pontius Pilate was very surprised when he learned that Jesus was already dead. For these reasons, there has been a lot of speculation about how he finally died.
Medical experts aren't completely sure about the usual cause of death in ancient crucifixions. An older theory holds that the fixed position on the cross would cause blood to slowly accumulate in the legs, and the lack of blood elsewhere would gradually lead to death. One problem with this theory is that the victim usually wasn't completely immobilized on the cross. Although his ankles and hands were in fixed positions, he did have some freedom to move up and down vertically by bending his knees.
According to the preferred modern theory, the victim had to push up with his legs to hold himself in a free-breathing position, and he would slowly suffocate when he became too exhausted to continue holding himself up. This theory is supported by the fact that Roman soldiers sometimes hastened death by breaking the victim's legs.
But whatever the cause, it normally took much longer than six hours for the victim to die. For this reason, many experts think that a special factor was involved in Jesus' death.
One obvious possibility is wounds or injuries. The gospels say that Roman soldiers flogged Jesus and pressed a crown of thorns onto his head before the crucifixion. In addition, the gospel of John says that nails were used to attach him to the cross.
If the flogging was especially brutal, or if the other wounds were unusually severe, an excessive loss of blood could have brought about an early death. But blood loss normally leads to unconsciousness and a gradual death, whereas the gospels indicate that Jesus remained fully conscious throughout the ordeal and then died abruptly. Thus, excessive bleeding probably wasn't the cause.
There are several possible explanations for an abrupt death, including heart attack, heart rupture, stroke, shock, and blood clot. Some experts think that the last of these, a blood clot, was the most likely cause of Jesus' death. But there isn't enough information to be certain about the matter.
According to John 19:34, after the Roman soldiers found that Jesus was dead, one of them thrust a spear into his side to make sure. But if the account is correct, Jesus was already dead when this happened. (The other gospels don't mention this incident.)
Some people have suggested that Jesus himself chose the moment of his death by "simply dying", or possibly by stopping his own heart from beating. Another possibility is that God didn't want to watch him suffer any longer and mercifully brought the ordeal to an end.
Note: The accounts indicate that Jesus had wounds on the hands and ankles (from nails), in the side (spear thrust), on the head (crown of thorns), shoulders (from carrying the cross) and back (flogging). Wounds or markings in these same locations sometimes appear on mystics or other individuals who are very close to God. Called stigmata, they are often said to be a supernatural sign of holiness. But although they may bleed for a while, they normally aren't fatal.
Note: For a discussion of ancient crucifixions, go to this article about How Jesus Died