Bill Hicks used to do a routine about the irony of Christians wearing crosses - "Nice sentiment, but do you really think when Jesus comes back, he's really going to want to look at a cross? Ow! Maybe that's why he hasn't shown up yet. (As Jesus) 'I'm not going, Dad. No, they're still wearing crosses - they totally missed the point. When they start wearing fishes, I might go back again.'." (Bill Hicks, Love All the People, p. xi).
As you'd expect, Hicks had done his research; early Christianity used a fish as its - if you like - logo. The rise of the crucifix coincides roughly with the church's adoption by Imperial Rome, and its move from underground to establishment status. We're so used to the church identifying itself by a means of execution that we forget how odd it is - if Jesus had been hanged, would priests wear a little gallows round their necks?
Of course, a cross is a much more powerful icon than a gallows - the intersection of horizontal and vertical lines symbolises the coincidence of the human and divine that is, to Christians, the significance of Jesus, the 'word made flesh'. Christianity doesn't have a premium on this idea - according to the film-maker and ethnographer Maya Deren, the poteau-mitan, a vertical pole at the centre of a voodoo temple, carries the same symbolism:
'The sign of the cross appears everywhere, whenever communications of traffic between the worlds is to be indicated. The vertical dimension comprehends both the abyss below and the heavens above the earth, the dimension of infinity; the horizontal comprehends all men, all space and matter.' (The Voodoo Gods, p.43)
A crucifix isn't simply a cross, though - it has the additional element of a human body. Part of the image's power comes from the contrast between the precise right angles of the cross and the messy curvature of the tortured, semi-naked figure. (It would be disingenuous to deny that there's also a sexual element - Western Art only allows the male body to be celebrated in the contexts of suffering and war.)
The crucifix epitomises one of the central tensions of human life - between the right angles of the ideal, and the curvature of the organic. The mathematician Piet Hein wrote that 'In the whole pattern of civilisation there have been two tendencies, one towards straight lines and rectangular patterns and one towards circular lines.' (quoted in Alex Bellos, Alex's Adventures in Numberland, p. 209). Hein devised a mathematical figure - the superellipse - that was designed to satisfy both tendencies. It was adopted as the model for Danish road layout.
You see this tension in surprising places; it's the basis for most modern dance music, which balances electronic beats with very human, soul-based vocals - the template was laid down by the collaborations between Giorgio Moroder and Donna Summer. Going back a bit further, Jerry Lieber and Mike Stoller made history when they added strings to the Drifters' 'There Goes My Baby' - Jimmy Webb even used quasi-religious language to describe it: 'Rock 'n' roll and the string ensemble are not antithetical after all. To the contrary, the rough, self-taught textures of rock vocalists are ineffably complemented by the silken tones of the orchestra and vice versa.' (quoted in Ken Everson, Always Magic in the Air, p. 60, my italics).
Most methods of execution - hanging, stoning, beheading, the electric chair - carry a deliberate aspect of physical humiliation. Only crucifixion and the firing squad allow a degree of dignity - that other most pictorialised of martyrs, St. Sebastian, died by an early version of the latter. It's sobering to consider that Pontius Pilate may have helped ensure Christianity's survival when he condemned its prophet to a painful, but aesthetically pleasing, form of death.