When archaeologists on a dig in southern Portugal last year flipped over a heavy chunk of slate and saw writing not used for more than 2,500 years, they were elated.

The enigmatic pattern of inscribed symbols curled symmetrically around the upper part of the rough-edged, yellowish stone tablet and coiled into the middle in a decorative style typical of an extinct Iberian language called Southwest Script.

"We didn't break into applause, but almost," says Amilcar Guerra, a University of Lisbon lecturer overseeing the excavation. "It's an extraordinary thing."