But deep inside, they found a wooden stockade, what looked like a primitive electric chair, photos of burned bodies amid reams of surveillance documents. Five tiny cells weren't just to imprison people, it seemed, but to torture them.
"It looks a bit too much like Nazi Germany to me," said Capt. Pete McAleer, commander of Echo Company of the 15th Marine Expeditionary Unit, whose patrol found the small compound.
Across Iraq, coalition troops are finding glimpses of past horrors — suspected torture chambers, secret police headquarters, Iraqis who reveal scars to show the cruelty of Saddam Hussein's rule carved onto their bodies.
At a prison in Basra, Iraqis showed journalists a white stone jail known as the "White Lion" where they claim Saddam's secret police for decades tortured inmates with beatings, mutilations, electric shocks and chemical baths.
"They did unthinkable things — electrocution, immersion in a bath of chemicals and ripping off people's finger- and toenails," resident Hamed Fattil told British reporters.
Outside the jail, a man showed Associated Press Television News his mangled ears — he said Iraqi police cut them off.
Fattil said Iraqi police locked him and his two brothers in a jail dungeon in 1991, and that he was freed after eight months but his brothers were still missing.
Human rights groups and exiled Iraqis have long claimed that Saddam ran a regime built on torture and intimidation.
In Nasiriyah, McAleer said they believed the building they found was used by Iraqi police or Baath party security forces to hold and torture prisoners, and to keep documents and identification cards to monitor local residents. Some cards showed pictures of small children; it was not clear why.
"The records were very detailed," said McAleer. The compound was surrounded by a wall that included hand-painted outlines of people and tanks to use for target practice.
Deep inside the building, there is a small room with no natural light with five tiny cells, all with heavy barred doors.
In one, a wire was connected to a small hand-cranked generator and steel bar. Marines who searched the building said it had also been connected to a steel chair in what appeared to be a primitive electric chair.
"Who knows what they did with that steel rod," McAleer said.
Lance Cpl. James Jeffreys, of Oxnard, Calif., said the room also had a type of wooden stock, where a rope could be wrapped around a prisoner's neck, laced through holes in the wood, and then back to bind a prisoner's hands.
"I believed it to be a police substation, but as soon as I got back in there I thought (of a torture chamber)," he said.
Elsewhere in the building, the floor was strewn with clothing, medicine and documents — including photographs of badly burned human bodies, Jeffreys said.
"From the position of the bodies, it looked like they could have been (burned) alive," said Jeffreys. Key documents and photographs that could be salvaged during the short initial search were turned over to a higher headquarters.
Much of the building's clothing and medicines were burned in a fire. McAleer said he believed the fire was set by local residents after the Marines first checked the building to rid their community of the torture chamber and its instruments.
"We have seen this done before," said McAleer. "Once the locals know it is safe, they will come in and destroy" such police and government compounds.
In Basra, Associated Press Television News captured footage of a jail basement that was a warren of cells, chambers and cages.
For the cameras, two men re-enacted how jailers allegedly tortured prisoners.
One man, hands tied behind his back with a rope attached to a hook on the ceiling, bent over while another man pantomimed hitting him on the back and the face with his hands and a long, white rod.
One man shuddered while the other gave him a pretend electric shock.
Fattil took British reporters into a yard behind the jail to see a set of white boxy cells, surrounded by red wire mesh with a low, wire roof.
Some cells were used to hold women and children. Hundreds of men were kept in a single cell about the size of a living room with one rusted grate window, he said.
Between the men's and women's cells was a long mesh cage. Hamed said here, jailers pressed prisoners against the mesh and squeezed hot irons against their backs or threw scalding water on them in front of other inmates.
"It was a place of evil," he said.