Why Was Jesus Crucified? - A historical perspective:
It's rather clear what St. Paul meant by saying that "the preaching of the cross is foolishness" to most people of his day. As Martin Hengel showed in Crucifixion in the Ancient World and the Folly of the Message of the Cross, Roman-era writers deemed crucifixion the worst imaginable fate, a punishment of unspeakable shamefulness. Celsus, a Roman critic of Christianity, ridiculed Christians for treating as divine someone who had been crucified. A second-century anti-Christian graffito from Rome, well-known among historians who study the time period, depicts a crudely drawn crucified man with a donkey's head; under it stands a human figure, and beneath this is a derisive scrawl: "Alexamenos worships his god."
There was, in short, little to be gained in proclaiming a crucified saviour in that setting in which crucifixion was a grisly reality. Some early Christians tried to avoid reference to Jesus' crucifixion, while others preferred one or another alternate scenario. In one version, in a Christian apocryphal text, the soldiers confuse a bystander with Jesus, crucifying him instead, while Jesus is pictured as laughing at their folly. This idea is likely also reflected later in the Muslim tradition that a person from the crowd was mistakenly crucified as Jesus escaped. Many devout Muslims believe that Jesus was a true prophet, so it is simply inconceivable that God would have allowed him to die such a shameful death. Clearly, at least some early Christians felt the same way.