A trio of prisoners managed to get onto the roof of Swansea Prison where they remained for several hours, authorities said. It was unclear how they gained access on the morning of 17 April, and it took specialist officers several hours to get them down.
Eyewitness Sophie Price tweeted about her shock at seeing the men on the roof.
"Can't believe there's prisoners standing on Swansea prison roof kicking off never heard so much shouting in my life," she said.
Another, Bob Griffiths, from Bridgend, who saw the men on the roof, told the BBC they were shouting at each other and other prisoners were shouting at them from the cells. One of the men was spotted holding a bottle.
Others tweeted pictures from the scene.
Specialist prison staff had worked to "resolve this as quickly and safely as possible" and the offenders were now down, a Prison Service spokesman said, adding that they got onto the roof at around 9:50am BST.
Gathering crowds of onlookers were moved on from outside the prison and the Prison Service added that the prisoners had voluntarily come down.
Cigarette ban death
The prison has hit the headlines in recent months after a family blamed a smoking ban at the institution for a prisoner's death.
Dean George, 40, was found unresponsive in his cell a week ago. The partner of another inmate claimed it was in relation to the smoking ban, according to the South Wales Evening Post. There were two cell fires there at the end of last year.
The rooftop protest was reminiscent of the 1990 riot at Her Majesty's Prison Manchester, commonly known as Strangeways. Then a number of prisoners got onto the rooftop, where they spent almost three weeks.
The IBTimes UK has contacted the Ministry of Justice for comment. South Wales Fire Service also declined to comment.