Environment : Spain’s Falling Arches : Pollution is eating away at the ancient Roman Aqueduct in Segovia. City officials are racing to save the crumbling monument--its 163 arches and 20,000 stone blocks.

SEGOVIA, Spain — In this fairy-tale town rising above the parched expanse of central Spain, all roads lead to the Roman Aqueduct.

Too many roads.

The granite monument, choked in exhaust from cars and trucks rumbling through its massive arches, is crumbling--just shy of its 2,000th birthday. And the aqueduct--perhaps the finest of its kind--has become a new battleground in the war to save Europe’s architectural heritage. Like the Colosseum in Rome and Notre Dame Cathedral in Paris, the aqueduct is besieged by a silent yet implacable enemy--air pollution.

“We caught it just in time,” said Luciano Municio Gonzalez, an archeologist with the regional government of Castilla Leon, which sprang into action to save the aqueduct when its weakened state was discovered in mid-July.

Most traffic has been rerouted to cut unnecessary pollution and vibration, while scaffolding has been erected to support the aqueduct’s central arches. A team of experts working from the bucket of a yellow crane is examining the aqueduct’s estimated 20,000 stone blocks, one by one, to decide how best to arrest their deterioration.

Making matters worse are hundreds of darting, swallow-like swifts that nest in the aqueduct’s many cavities: Their abundant droppings seem to be acidic.

Officials promise they will do whatever it takes to save the aqueduct, a monument so synonymous with the town’s identity that its image has been emblazoned on the municipal coat of arms.

“Segovia without the aqueduct wouldn’t be Segovia,” said Felix Hernandez, a waiter at Meson de Candido, a restaurant in the shadow of the monument.

Assembled without mortar sometime during the first century after Christ, the aqueduct carried river water to the town without interruption until 1972, when engineers rechanneled the supply entirely though underground conduits.

Spanning a bowl-shaped valley, the two-tiered, bridge-like structure stretches more than half a mile and tops 95 feet at its highest point. Its massive gray columns, like the legs of a giant elephant, dominate the quiet neighborhoods that flank it.

“It is a monument of worldwide importance,” said Alonso Zamora Canellada, director of Segovia’s soon-to-open Fine Arts Museum. “Like the Eiffel Tower, Notre Dame or the Pyramids, it is unique.”

During the Middle Ages, when superstitious locals had all but forgotten their Roman benefactors, the aqueduct’s construction was commonly attributed to the devil, a story Segovian schoolchildren still learn today as part of local history. According to this legend, an old priest wagered his soul that the devil could not guarantee Segovia a fresh-water supply for eternity, and do the job in one night. The devil took the challenge.

Satan was just about to place the last stone of the aqueduct’s 163 arches when dawn broke, the legend says.

Too late.

Modern historians now believe that the aqueduct was built over several years, perhaps during the reign of Emperor Trajan (AD 98 to AD 117), himself a native of Spain.

The ambitious engineering project, like many others undertaken by the Romans, was intended to pacify and civilize recently conquered peoples by showing them the advantages of Roman rule, Zamora said.

“Besides carrying water, it had a clear political end: the diffusion of Roman culture,” he said.

Nearly 2,000 years later, the aqueduct is again affecting politics in this town of 54,000: Responding to local pleas, officials in Madrid say they will forge ahead on a long-planned, $35-million ring road around Segovia.

“This project would have waited 10 or 15 years,” said Javier Garcia-Arevalo Ceprian, a spokesman for Segovia’s conservative city government.

Meanwhile, most locals crawl through traffic jams on roundabout detours with a sense of prideful sacrifice, at least for now.

More than local history is at stake, of course; tourism is one of Segovia’s main industries.

The aqueduct, which U.N. officials declared to be a “Patrimony of Humanity” in 1985, is only one of the town’s many architectural treasures.

A storybook castle and a magnificent 16th-Century cathedral also combine to make walled Segovia a must-see for day-trippers from Spain’s capital, Madrid, 55 miles to the southeast.

“This is the kind of thing you see in movies,” said Canadian tourist Nonni Lund, noting the aqueduct’s spectacular scale.

Despite the recent commotion, many locals say they aren’t really worried about the aqueduct’s future. It has stood the test of time, they say.

“It’s been like this for 2,000 years,” said Maria Jimenez, a lace-maker. “It’s not going to fall down all of a sudden.”

Then a bus rumbled by, spewing exhaust.