There have been a handful of excellent studies on crucifixion circa Jesus’ context in the past ten years. Here are two monographs to consider: Samuelsson and Chapman. Unfortunately too many folks still fumble a bit with vague explanations of crucifixion. I've done a bit of fumbling myself at times. The popular notions of crucifixion as "the slave's death" and as "reserved for insurrectionists" are perhaps close to the mark, but not quite as helpful as they could be. As these two vague descriptions stand, it is hard to see how both could be true without qualification. I've previously attempted to explain that we see a particular status demotion to enemies of the state in crucifixion. In other words, the victims might have aspired to grandeur, but died as slaves. But I don't think that this quite hits the mark either.
Last week I was reading an essay by Joel Marcus published in 2006. Marcus writes:
"…this strange exalting mode of execution [crucifixion] was designed to mimic, parody, and puncture the pretensions of insubordinate transgressors by displaying a deliberately horrible mirror of their self-evaluation. For it is revealing that the criminals so punished were often precisely people who had, in the view of their judges, gotten "above" themselves. Rebellious slaves, for example, or slaves who had insulted their masters, or people of any class who had not shown proper deference to the emperor, not to mention those who had revolted against him or who had, through brigandage or piracy, demonstrated disdain for imperial rule. Crucifixion was intended to unmask, in a deliberately grotesque manner, the pretension and arrogance of those who had exalted themselves beyond their station; the authorities were bent on demonstrating through the graphic tableau of the cross what such self-promotion meant and whither it led. Crucifixion, then, is a prime illustration of Michael Foucault’s thesis that the process of execution is a “penal liturgy” designed to reveal the essence of the crime. …. The greater the insolence, the higher the cross; the proper response to excessive haughtiness was, in the words of the Clint Eastwood film, to "Hang ‘Em High!" (“Crucifixion as Parodic Exaltation,” JBL 125 : 73-87, here pp. 78-79.)