A medical doctor provides a physical description:
The cross is placed on the ground and the exhausted man is quickly
thrown backwards with his shoulders against the wood. The legionnaire
feels for the depression at the front of the wrist. He drives a heavy,
square wrought-iron nail through the wrist deep into the wood. Quickly
he moves to the other side and repeats the action, being careful not to
pull the arms too tightly, but to allow some flex and movement. The
cross is then lifted into place. The left foot is pressed backward
against the right foot, and with both feet extended, toes down, a nail
is driven through the arch of each, leaving the knees flexed. The victim
is now crucified.
As he slowly sags down with more weight on the nails in the wrists,
excruciating fiery pain shoots along the fingers and up the arms to
explode in the brain -- the nails in the wrists are putting pressure on
the median nerves. As he pushes himself upward to avoid this stretching
torment, he places the full weight on the nail through his feet. Again
he feels the searing agony of the nail tearing through the nerves
between the bones of his feet.
As the arms fatigue, cramps sweep through his muscles, knotting them
deep relentless, and throbbing pain. With these cramps comes the
inability to push himself upward to breathe. Air can be drawn into the
lungs but not exhaled. He fights to raise himself in order to get even
one small breath.
Finally, carbon dioxide builds up in the lungs and in the blood stream,
and the cramps partially subsided. Spasmodically, he is able to push
himself upward to exhale and bring in life-giving oxygen.
Hours of limitless pain, cycles of twisting, joint-renting cramps,
intermittent partial asphyxiation, searing pain as tissue is torn from
his lacerated back as he moves up and down against rough timber. Then
another agony begins: a deep, crushing pain deep in the chest as the
pericardium slowly fills with serum and begins to compress the heart.
It is now almost over. The loss of tissue fluids has reached a critical
level. The compressed heart is struggling to pump heavy, thick, sluggish
blood into the tissues. The tortured lungs are making frantic effort to
gasp in small gulps of air. He can feel the chill of death creeping
through his tissues.
Finally, he allows his body to die.
All this the Bible records with the simple words,
"and they crucified Him" (Mark 15:24).