The oldest civilization of ancient Mexico and Central America has finally yielded solid evidence of a writing system. Researchers who analyzed a stone block covered in a sequence of faint symbols have declared it the oldest conclusive writing sample from the New World, dating to around 900 B.C. or earlier and belonging to the region's oldest complex society, the Olmec. "Imagine if you will this extraordinary civilization that we've known about for 100 years suddenly to become literate. It gives them a voice in a way that's not directly accessible through artifacts alone," says one of the analysts, anthropologist Stephen Houston of Brown University. He and his colleagues report their conclusions in the September 15 Science.

The Olmec, who are famous for having carved heads up to eight feet tall out of rock, held sway in so-called Mesoamerica, along the Gulf of Mexico, from 1200 to 400 B.C. They constituted a major civilization, having several large cities and outposts as well as irrigation, iconography and a calendar. Signs of writing were strangely lacking, however, except for some controversial claims based on limited imagery. The block Houston and colleagues studied was recovered a decade ago from a gravel quarry at Cascajal, part of Veracruz, near what was the Olmec capital. Made of the mineral serpentine, the 36-centimeter-tall block has 62 images carved into it in a series of lines. Based on similarity to images in Olmec iconography, the researchers dated the block's inscription at 1000 to 800 B.C.

"We think it's writing because it's linear," Houston says, and because of the way the images are organized. Many of the shapes, which tend to resemble corn, insects or man-made objects, are repeated up to four times in the sequence. Several pairs of images crop up more than once, suggesting to the researchers a common feature of Mesoamerican languages called a poetic couplet.

Although such inferences remain speculative, other experts are convinced the markings represent writing. "This is cool," says William Saturno of the University of New Hampshire. "We now know definitely the Olmec had a fairly developed writing system. It's something we thought should exist, but we've never seen it."