LISBON, Portugal -- Hundreds of newly discovered rock engravings, hewn 20,000 years ago in what may prove to be the world's largest outdoor gallery of prehistoric art, fill the valley of the Coa River in northern Portugal.
The engravings of animals, including horses, wild goats and aurochen, the Paleolithic ancestors of cattle, were inscribed on outcroppings along both sides of the valley by nomadic hunter-gatherers toward the end of the last Ice Age.
They have come to light after environmental-impact research for a nearby $330 million dam under construction by the state electric company. The project will drown the valley under 300 feet of water once the dam is complete in about four years.
Scrap the dam to save hard-to-get-to, hard-to-see engravings? Flood the art to give Portugal more electricity and greater control of its water supplies?
Portugal, wed to development and sprinting to catch up with the rest of Europe after half a century of dictatorship, is not used to grappling publicly with such questions.
But for the first time in this young democracy, the inevitable confrontation between tomorrow's needs and yesterday's legacies is provoking national debate over rival claims on the environment and the economy.
"Under dictatorship, things were destroyed and people didn't care," political analyst Alvaro Vasconcelos said. "An ancient Roman encampment swept away for an airport, an 800-year-old Romanesque church gutted at the caprice of an ambitious parish priest. But times are changing."
What is being tested is whether, in changing times, it is possible for grass-roots pressure to save the art in the face of expensive technology.
"I think they will build the dam, because I am not accustomed to seeing people who have power in this country abdicate it for these kinds of reasons," said Jose Luis Ramos Pinheiro, news director at the country's biggest radio station. "Ten years ago we would never have heard about the engravings. In another 10 years maybe it would be possible to stop the dam."
First official word of the engravings came in a one-line mention to a government agency in a 1993 report from an archaeologist commissioned at agency behest and power company expense to conduct a required survey of the valley.
The archaeologist, now under heavy criticism, is accused of planning to keep his findings secret until he was able to publish them.
Neither did the government agency, called IPPAR, which is charged with protecting Portugal's archaeological and architectural heritage, show much enthusiasm to publicize or evaluate the finds.
Critics now charge a cover-up. IPPAR, or Portuguese Institute for Architectural and Archaeological Patrimony, and the electric company deny that.
Designed to create a backup reservoir to regulate water levels at five other dams on the nearby Douro River, the Coa dam is being built by Electricidade de Portugal, the giant, government-owned utility.
The first findings were in a 600-foot stretch along one side of the valley. Many animals are chiseled shapes. Others are represented in outline forged in the softer rock in a foreboding region of the Iberian interior, where until recently scientists doubted there had been Paleolithic, or early Stone Age, settlement.
The engravings are the scratchings-and-chippings witness of a Cro-Magnon people of whom there is as yet no other trace.
Is the art a bellies-full celebration by successful hunters? A religious appeal for food? A deer-up-the-valley sort of signpost? Or simply a decorative reproduction of nature by a primitive people? Some are quite moving; a pair of ancient horses nuzzling. In dull light on weathered rock, others are hard to make out.
There are no roads into the area, and few people live nearby. Access is by boat or old sheep trails, but since reports of the engravings surfaced, professional and amateur prospectors have discovered a series of engravings on discontinuous outcroppings along more than 10 miles of valley side.
"The number of engravings is growing every week," said Joao Zilhao, a University of Lisbon professor of prehistoric archaeology. "We now have at least 200 large hammered ones. For each of them there may be 30 or 40 finely incised figures that are hard to see.
"I think we are talking about the largest and oldest open-air Paleolithic site in the world," said Mr. Zilhao, who is leading academic attempts to stop the dam.
Jose Morais Arnaud, president of the Association of Portuguese Archaeologists, said that after some initial differences of opinion over the merits of the engravings, there is unanimity among Portugal's 200 archaeologists that the engravings must not be drowned.
The electric company defends the new dam, planned to hold 450 million cubic meters of water. The company said that with contracts already signed, it costs no more to continue than to stop, but the engravings' defenders fear that they are watching a fait accompli.
"The situation is not very promising. The electric company is working 24 hours a day," Mr. Arnaud said.