Crucifixion was a method of execution employed by the Romans until around the 3rd century. So agonizing and horrible was this form of death, that from it we get our english word "excruciating". It was a disgraceful and dishonorable death since the body was left on the cross after death rather than being buried honorably.  It was usually reserved for slaves or common criminals. Roman citizens were not typically executed in this way. This is the method by which Jesus Christ was killed.

Crucifixion consists of nailing or tying the condemned to a "T" shaped cross, typically by the outstretched  hands (wrists) and feet. The condemned would often have to carry either the entire cross or the cross bar to the place of execution. They would also usually have been severely flogged, scourged or whipped before, as was the case with Jesus.

One of the main reasons why crucifixion was so horrible is that it could take days for the victim to die. During that time, it was believed that the position of the arms made it difficult to breathe. The victim typically had to spend their time choosing to relax the weight on their arms, making it nearly impossible to breathe, or to lift themselves up by the arms, causing incredible pain in their hands. The cause of death was usually asphyxiation, though shock from loss of blood, dehydration and exhaustion would also contribute. If the victim was taking too long to die, occasionally the Romans would break their legs to hasten the death, but this was not done to Jesus as He died on the cross more quickly than usual, perhaps due to his severe wounds from the flogging.