Crucifixion itself doesn't kill you. Sure you keep passing out from the shock in the beginning, and if they don't control the blood loss or infection, you're in trouble, but it's exposure and dehydration that used to really get the the Roman prisoners. The point of crucifixion is that some one has to walk past that guy on a cross to work, and then has to walk past him again on the way home, and then past him on the way to work the next morning again. Like an advertising billboard it's all a question of exposure and saturation. But here's where the Romans were really assholes, they would feed the lads on the crucifix, give them a little water too so that it would last even longer and even let the convict off for a while now and then, but they'd have to break their legs first. Apparently (According to my art history teacher preaching about the legend of the true cross.) this is what they they offered Jesus. A couple hours off the cross in exchange for some broken legs because no one could be bothered running after him if tried to make a break for it, but there was some prophecy that the messiah never having broken any bones so Jesus immediately magically willed himself dead rather than break prophecy, but do you want to know what I got out of that story?
Jesus Christ committed suicide.