As a waypoint on the ancient Silk Road, the metropolis of Palmyra had it all, broad towers, impressive temples and enviable trade. Water from local wells even contained fluoride, limiting that scourge of the ancients — tooth decay.

But just as the wealth of Palmyra vanished, leaving behind ruins in the Syrian desert, a new study suggests its waters may also have been ruinous in the end for the city's inhabitants.

Palmyra today is a World Heritage Site, a designation bestowed by the United Nation Educational, Scientific and Cultural Organization in 1998. About 140 miles southeast of Damascus, the trading town known as Tadmor to the ancients, later Palmyra, had been a center of trading since around 2000 B.C. But the town really bustled during the Roman Empire, and was filled with magnificent buildings throughout the 1st and 2nd century, starting during the reign of Roman emperor Hadrian in 129 A.D.

He renamed the oasis town "Palmyra Hadriana." Modest guys, those Roman emperors. The city's wealth faded with the decline of Roman influence in ancient Syria.

Starting in 1990, Japanese archaeologists have been excavating the Southeast Necropolis of Palmyra and examining remains from the Roman era. Despite Palmyra's prosperity, "skeletal remains uncovered from the underground tombs of Palmyra have been found to retain an arthropathy of the joints, especially in the knee joint, bone fracture, marked bone lipping, spur formation, and eburnation (smoothed bone cavities)," reports the team led by Kiyohide Saito of the Archaeological Institute of Kashihara in the current Journal of Archaeological Science.

Fluoride in small concentrations is thought to deter microbes that cause tooth decay, the reason why about 66% of public water supplies in the United States are now fluoridated, according to the federal Centers for Disease Control and Prevention. But the Palmyrans' symptoms, along with discolored teeth, point to "fluorosis," a skeletal and enamel-damaging syndrome caused by ingesting too much fluoride over a long time, the researchers note. Looking at two large tombs for example, 25 of 33 individuals (76%) had discolored teeth in one, and 45 out of 65 (69%) had discolored teeth in the other.

Palmyrans drank, and still drink, water from wells tapped from ground water by long tunnels called "qanats" (an excellent Scrabble word). The area's geology and water table has been stable for about 7000 years, meaning water conditions now aren't greatly different from those during Roman times. In a bid to estimate the fluoride burden suffered by the town's ancient inhabitants, the researchers analyzed the water from these wells. Fluoride levels were as high as three parts per million in the water, a level that a National Academy of Sciences report in March warned could lead to fluorosis.

To further check, the archaeologists also ground up seven discolored teeth from tomb inhabitants, and compared them to seven others without discoloration, to reveal their fluoride concentration. In a chemical reaction, fluoride tends to replace some calcium in tooth enamel, making overexposure to fluoride particularly worrisome for children with growing teeth and bones. The ground-up teeth revealed that in the most discolored ones, about 22% of the calcium had been replaced by fluoride. "Thus, it was possible to directly verify that the ancient inhabitants of Palmyra did suffer from fluorosis," they conclude.

Although the plight of these long-gone people may seem merely of academic interest, concern about fluorosis exists today. U.S. Public Health Service standards call for fluoridated water to not exceed 1.2 ppm in drinking water. But about 200,000 people nationwide drink water with levels above 4 ppm, tapped from wells naturally high in fluoride, according to the National Academy of Sciences report. About 10% of kids in towns with these water supplies develop severe tooth enamel discoloration from fluorosis, weakening their teeth. The report also raised concerns about such high levels of fluoride being linked to bone fractures, like those suffered by the ancient Palmyrans, but it did not come to any final conclusions.