The recently discovered art works - engraved on rock faces between 19,000 and 23,000 years ago - are in a valley about to be flooded as part of a hydro-electric dam project.
The carvings are among the most important prehistoric art-works ever to have come to light in Europe - and intense academic pressure is building up on the government to save them. But the authorities face a dilemma. If they allow the engravings to be drowned, they are likely to be damaged by water erosion. Yet if they scrap or scale down plans for the project, some local people - hungry for jobs and prosperity - have threatened to destroy the carvings.
It is not yet clear whether a third alternative - moving the engraved rock faces to higher ground - would be technically or financially feasible.
Around 100 carvings, mostly of animals, have been discovered at the site - in the Coa valley near Villanova de Foz Coa, 200 miles north-east of Lisbon.
Archaeologists believe that a further 100 to 200 still await discovery and are urging that a full survey of the valley should be carried out.
The Stone Age engravings - mostly carved in naturalistic style - depict aurox (wild cattle), horses, ibex and red deer (both stags and does). Some patches of much-worn red paint also survive - suggesting that originally the valley was also home to Stone Age paintings as well as engravings.
Like many prehistoric rock sites, these recently-discovered art-works are located near the confluence of two rivers. It is likely that this was in some way related to the probable ritual function of the valley.
Certainly the place seems to have retained its sacred nature for thousands of years, either continuously or intermittently, for among the art-works, archaeologists have found 4,000-year-old Bronze Age engravings of deer and 2,000-year-old Iron Age engravings of warriors.
The Coa valley site is the largest open air collection of substantial Palaeolithic (Old Stone Age) engravings in the world. Its discovery follows on the heels of another Iberian Palaeolithic rock-art find five years ago when archaeologists came upon a large number of animal engravings 10 miles south of Coa at Siega Verde in Spain.Reuse content