The earliest depiction of a crucifixion, possibly 1st century AD [source].
Yesterday was Good Friday, the day Jesus was crucified, and there was plenty of Blog and press coverage of crucifixion - a lot of it very superficial.
Rogue Classicist was an exception - he covered an article in a medical journal about ancient crucifixion methods. He pointed out that there is no reason Christ was not crucified as depicted in art, and that evidence from the Bible suggests that an upright crucifixion was most likely. If it ain't broke, why fix it: www.atrium-media.com/rogueclassicism//Posts/00003439.html
The medical article is available as a PDF here: www.rsm.ac.uk/media/pdf/j06-04crucifixion.pdf
See also an old New Scientist article on the cause of death in crucifixions: www.newscientist.com/article.ns?id=lw195
Christians are meant to contemplate the Crucifixion today and tomorrow, before the miracle of the Resurrection. So here goes.
There are many mentions of crucifixion in ancient texts, but they give us few details of how it was actually done. As far as I know, it was first recorded as practised by the Greeks: Pericles crucified the ruler of Samos when he captured the island. Alexander the Great crucified the survivors after the siege of Tyre, then Hephaestion's doctor for failing to keep him alive. Herodotus claimed, like everything bad, that it was originally Persian.
The Romans took it to extremes - we all remember the ending of the film Spartacus, which was based on historical sources that tell us Crassus crucified Spartacus' 6,000 followers along the Via Appia. In the previous Servile Wars in Sicily, crucifixion was also used to punish the slaves, and this method of death is generally associated with slaves. Cicero also have an account of Lucius Domitius Ahenobarbus as governor crucifying a Sicilian slave for having killed a boar with a spear (97 BC); slaves on the island were not allowed to carry weapons, and his death was designed to serve as a deterrent to others. Roman citizens seem not to have been crucified, as it was seen as a demeaning and dishonourable way to die. An exception is when Fimbra crucified Roman deserters in Asia during the Mithridatic Wars (Dio): the point he was making was that by refusing to fight they were worse than slaves.
During the Empire, the practice continued. Tiberius hated oriental cults, so when he closed the temple of Isis in Rome (AD 19), he ordered her priests crucified. A few years later, Christ was crucified in Jerusalem. Josephus wrote about crucifixions around the walls of Jerusalem; during the AD 70 Jewish revolt he says that some garrisons preferred to surrender. It seems to have been common in eastern provinces during the first century AD.
In 313 Constantine issued the Edict of Milan; Christianity was allowed, prosecution of Christians ceased. Eusebius tells us that he banned crucifixion soon after.
In modern history there are a few instances when crucifixion was used as the means of death. The Japanese banned Christianity, and to punish those who broke the law chose to crucify some Christians at Nagasaki in 1597 - the irony of this form of death could not have been lost on the Jesuits and Franciscans being martyred. Crucifixion seems to have been chosen as a way to kill Missionaries in other areas too. Christians in some towns in Mexico and in the Philippines still hold mock crucifixions each year on Good Friday.
Although many were crucified, the deliberate dishonour and punishment of their deaths means that few were buried in a way likely to preserve the evidence of crucifixion. Only one tomb, at Giv'at ha-Mivtar to the north of Jerusalem, has yielded physical evidence of crucifixion. See the article by Israeli archaeologist Joe Zias, with numerous illustrations.
The illustration above is probably the earliest known depiction of the crucifixion of Christ, the Alexamenos Graffito; the crucifixion is mocked in this caricature, and Christ given an ass's head. The inscription reads: "Alexamenos - worship your God !". It was found on the Palatine in 1857, and is now in the Palatine Antiquarium. Some date it to the first century AD: faculty.bbc.edu/rdecker/alex_graffito.htm. Others traditionally date the graffito to the third century, when Tertullian wrote of accusations that Christians worshipped an ass's head: "Somniatis caput asininum esse Deum nostrum" (Apol., xvi; Ad Nat., I, ii). The cross, and later the crucifixion, were depicted in Christian tombs, and we have many more examples after Christianity became the state religion.