The etchings cover more than half a kilometre of caverns and include more than 200 separate drawings. They were discovered at Cussac in September 2000 but the findings have only just been made public.

Experts believe they could be up to 30,000 years old. That would make them the second oldest examples of cave art, after the 32,000-year-old drawings found in the cave of Chauvet-Pont-d'Arc, in the Ardèche region of France. There is only one other good example of cave art older than 20,000 years, at Cosquer, also in France.

"It is as important for engraving as Lascaux is for painting," says Dany Baraud, chief archaeologist at the Regional Direction of Cultural Affairs of Aquitaine, referring to the oldest known example of prehistoric painting, found at a nearby site.

Archaeologists say the etchings at Cussac are unusual because they are very well preserved, quite sophisticated and include images of birds, mammoths and people.

"Humans are not normally depicted except in very schematic ways - for example, women may be portrayed as pubic triangles," says Andrew Lawson, director of the independent research group Wessex Archaeology in Wiltshire, UK. "It's usually stylised and not instantly recognisable."

Dating etchings can be a tricky task, adds Lawson. Unlike some primitive paints, there are no flakes of charcoal that can be radiocarbon dated.

Etchings are dated using assumptions about how the rock would weather over time, altering the rock crystals and changing their chemistry. Microbes on the rock surface also form a veneer known as "rock varnish" that adds to the alteration.

Experts are still analysing the dating evidence from Cussac, along with seven graves that were also found in the cave. If the skeletons turn out to be Palaeolithic, it will be the first evidence that people buried their dead in caves that were decorated by their contemporaries.

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