The contrapasso of the sorcerers, astrologers, and false prophets
by Stradanus
Contrapasso (or, in modern Italian, contrappasso), from the Latin contra and patior, “suffer the opposite,” refers to the punishment of souls in Dante’s Inferno “by a process either resembling or contrasting with the sin itself.“
One of many examples of contrapasso occurs in the 4th Bolgia of the 8th circle of Hell (Inferno, Canto XX), where the sorcerers, astrologers, and false prophets have their heads twisted around on their bodies backward, so that they “found it necessary to walk backward, / because they could not see ahead of them.” While referring primarily to attempts to see into the future by forbidden means, this also symbolises the twisted nature of magic in general. Such a contrapasso “functions not merely as a form of divine revenge, but rather as the fullfilment of a destiny freely chosen by each soul during his or her life.”
(from the Wikipedia entry on contrapasso)