After a prisoner was arrested, he was held in a cell then brought before a court which decided what to do with him. If he was found guilty of the charges and condemned to die by crucifixion, he was often flogged beforehand.
Flogging involved stripping the prisoner and tying his hands to an upright post. A soldier stepped forward with the flagrum in his hand. This was a whip with a short wooden handle and leather thongs with small pieces of metal attached to the end of each thong. The whip fell repeatedly on the condemned man's head, shoulders and body.
The metal pieces on the flagrum first bruised, then cut into the skin and subcutaneous tissues, producing first an oozing of blood from the capillaries and veins of the skin, and finally spurting arterial bleeding from vessels in the underlying muscles.
Finally the skin of the back would be gaping open and the entire area would become an unrecognizable mass of torn, bleeding tissue. This flogging was meant to punish, terrify and weaken the condemned man.
When it was time to go to the place of execution, a heavy beam of wood, the crossbeam, was placed across the man's shoulders, probably attached there by leather straps to prevent the weakened man from dropping it. The route taken by the procession of soldiers and condemned man was along a crowded street, so that his suffering was evident to as many people as possible - crucifixion was used as a deterrent to other citizens who might be tempted to commit the crime for which the condemned man was being punished.
At the place of execution, the condemned man was stripped naked, a further humiliation, and the beam across his shoulders was lowered to the ground. This threw his body backwards, because the straps or ropes tying him to the beam would still be in place. A soldier drove a heavy, square, wrought-iron nail through the wrist, deep into the wood. When both wrists had been nailed, the beam was lifted into place at the top of posts already lodged upright in the ground.
Many condemned men were left in this position, with their legs tied to the upright beam, but Jesus seems to have had his feet nailed to the woodas an extra punishment. It made his death more brutal, but it also made it quicker, since the additional agony sent him into shock, while also making it more difficult for him to push his body upwards, to breathe. He also lost more blood, weakening him further.
Since he was effect hanging by his arms, his chest muscles began to go into cramp. He could breathe in, but it became increasingly difficult to breathe out. Carbon dioxide built up in his lungs and in the blood stream. He was horribly dehydrated. The pericardium, the sac surrounding his heart, filled with fluid, compressing his heart, and he died of heart failure and suffocation.