HILLA, Iraq -- Maytham Hamzah cast his eyes toward the remains of King Nebuchadnezzar's guest palace in Babylon, one of the world's first great cities. He smiled, bitterly.

"They destroyed the whole country," Hamzah, the head of the Babylon museum, said of U.S. forces in Iraq. "So what are a few old bricks and mud walls in comparison?"

U.S. forces did not exactly destroy the 4,000-year-old city, home of one of the world's original seven wonders, the Hanging Gardens of Babylon. Even before the troops arrived, there was not much left: a mound of broken mud-brick buildings and archaeological fragments in a fertile plain between the Tigris and the Euphrates rivers.

But they did turn it into Camp Alpha, a military base, shortly after the U.S.-led invasion in 2003. Their 18-month stay there caused "major damage" and represented a "grave encroachment on this internationally known archeological site," a report released this month in Paris by the United Nations' cultural agency, UNESCO, says.

The ruins stretch over a rectangular area measuring 2,100 acres along the western banks of the Euphrates. The site consists of Nebuchadnezzar's palace, which then-President Saddam Hussein rebuilt in the 1980s; the remains of the Temple of Ninmakh; and a palace for royal guests. In addition, there is the Lion of Babylon, a 2,600-year-old sculpture, and the remains of the Ishtar Gate, the most beautiful of the eight gates that once ringed the perimeter of the town. It still bears the symbols of Babylonian gods.

According to the report, which comes after five years of investigation by a team of Iraqi and international experts, foreign troops and contractors bulldozed hilltops and then covered them with gravel to serve as parking lots for military vehicles and trailers. They drove heavy vehicles over the fragile paving of once-sacred pathways.

The report also says that forces built barriers and embankments to protect the base, pulverizing ancient pottery and bricks that were engraved with cuneiform characters. They dug trenches where they stored fuel tanks for their helicopters, which landed near an ancient theater. Among the structures that suffered the most damage, according to the report, were the Ishtar Gate and a processional thoroughfare. Experts also say troops filled their sandbags with soil from a site that was littered with archaeological fragments.

Bricks were looted as well -- both those of Babylonian vintage and newer ones that Hussein used to rebuild parts of the ruins. The latter variety was emblazoned with an ode to himself.

"The damage was so great," said Maryam Mussa, an official from the Iraqi state board of heritage and antiquities, which is in charge of the site. "It would be so difficult to repair it, and nothing can make up for it."

Spokesmen for the U.S. military in Iraq did not respond to requests for comment. But the military has previously said that looting would have been far worse had it not been for the presence of its troops. The military also said in 2005 that it had discussed setting up the base with Iraqi archaeologists in charge of the site.

The site has been closed to the public since 2003. Facing mounting criticism from archaeologists in Iraq and around the world, troops vacated it in summer 2004. It was reopened this June, despite warnings from experts that the ruins might suffer further damage unless they were first restored and given proper protection.

Many residents of Hilla, a town 60 miles south of Baghdad that sits near the ruins, said they have not been to the site because they can't bear to see the damage.