The ruling came in the case of Alabama guards who tied a prisoner to a "hitching post" for hours in the sun as a disciplinary measure.
Speaking for the 6-3 majority, Justice David Souter cited 1986's Whitley vs. Albers: "The unnecessary and wanton infliction of pain ... constitutes cruel and unusual punishment."
"Cruel and unusual punishments" are banned by the Eighth Amendment.
Writing for the majority, Souter said the treatment given the Alabama prisoner certainly fit that description.
"Despite their participation in this constitutionally impermissible conduct," Souter said, citing 1982's Harlow vs. Fitzgerald, the guards may still have escaped liability in court if their actions did not violate "clearly established" legal and civil rights "which a reasonable person would have known."
Souter said the "obvious cruelty inherent in this practice should have provided" the guards with that knowledge.
Thomas said the majority based its opinion "on facts not alleged, law not clearly established and its own subjective views on appropriate methods of prison discipline."
In the case that brought Thursday's rulnig, a federal appeals court earlier ruled that the hitching post punishment was cruel and unusual punishment -- banned by the Eighth Amendment -- but said the guards could not be held accountable.
The inmate, Larry Hope, told the Supreme Court in a petition that he was working on a chain gang near an interstate highway in May 1995 when another prisoner started an argument with him.
"Mistakenly concluding that the argument was Hope's fault, a correctional officer sent Hope back to the Limestone facility and ordered that he be placed on an outdoor restraining device known as the 'hitching post' for being 'disruptive to the work squad,' " Hope's lawyers said in their petition to the high court. However, Hope "neither refused to work nor incited other inmates not to work."
Hope's lawyers said his wrists were handcuffed "to a horizontal pole that was roughly the same height as his head -- in accordance with (a guard's) instructions," and was forced to stand for two hours until a correctional captain determined that the other inmate had started the argument.
A guard caught Hope asleep on the bus en route to a chain gang site in June 1995, the inmate's petition said, and "picked a fight" with him. Hope was "subdued, handcuffed, placed in leg irons and transported back to the prison, where he was placed on the hitching post" by a guard. Hope "was photographed by national news media that day, and photographs of his humiliation were published in The New York Times and Life magazine."
Hope's petition said he was left on the hitching post for about seven hours, standing with his wrists cuffed in a painful position, and mocked when he asked for water.
Hope eventually sued in federal court, but a U.S. judge dismissed the case, saying the guards were entitled to "qualified immunity" when they were performing their duties, much like police officers.
The federal appeals court agreed, saying even though Hope's constitutional rights were violated, the guards could not be brought to account.
Hope then asked the Supreme Court for review. He asked the high court to decide, among other things, whether there "are some cases, such as those involving torture, in which the constitutional right alleged to have been violated is so apparent that clarifying case law is neither available nor necessary in order to overcome a claim of qualified immunity."
Though Alabama may be alone in its use of the "hitching post," a number of states -- Missouri, Nebraska, Nevada, Oklahoma, Utah, Indiana, West Virginia, Mississippi, Louisiana, Hawaii, Pennsylvania, Oregon, Connecticut, Rhode Island, Idaho, and Guam -- asked the justices not to hear the case.
While not agreeing with Alabama's position, they said public employees needed some "breathing space" from lawsuits.
The Supreme Court heard argument in April, and reversed the lower court Thursday.
(No. 01-309, Hope vs. Pelzer, McClaran, Gates and Gates)