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."

For more than two centuries, scientists have tried to decipher Southwest Script, believed to be the peninsula's oldest written tongue and, along with Etruscan from modern-day Italy, one of Europe's first. The stone tablet features 86 characters and provides the longest-running text of the Iron Age language ever found.

About 90 slate tablets bearing the ancient inscriptions have been recovered, most of them incomplete. Almost all were scattered across southern Portugal, though a handful turned up in the neighboring Spanish region of Andalucia.

Some of the letters look like squiggles. Others are like crossed sticks. One resembles the number four and another recalls a bow-tie. They were carefully scored into the slate. The text is always a running script, with unseparated words which usually read from right to left.