The petroglyphs are carved in bas-relief in a sheltered grotto at the base of this red-basalt outcrop in Tien Shan, in Xinjiang, west China (Photo/Agencies)

The first scene shows nine massive females, each about two metres high, dancing arond in a circle, while a second transexual figure on the left is partially reclining as if about to fall into a trance (Photo/Agencies)

The second scene of the petroglyphs. It is believed that the larger-than-life hourglass figures that begin the tableau represent females, with their stylised triangular torsos, and shapely hips and legs (Photo/Agencies)

Many of the figures appear to depict transexuals combining both male and female features. Ithyphallic but wearing female headgear and chest decorations, they may depict shamans (Photo/Agencies)

The final scene, which appears according to one writer 'a lot like a frat party'. It shows 14 characters, seven of which have erect penises, apparently in the midst of a frenzied dance (Photo/Agencies)

These remarkable images show some of the earliest known examples of what we these days might dub pornography.

The Kangjiashimenji Petroglyphs, in Xinjiang, north-west China, depict an intense fertility ritual the likes of which is almost unique in the ancient world.

That's because while most prehistoric art presents images that are abstract and disembodied, this tableau appears to explicitly present our sex-crazed ancestors in the midst of a wild orgy.

The petroglyphs - thought to date back to the second millennium BC, although their exact age is difficult to determine - were discovered in the late Eighties by Chinese archaeologist Wang Binghua.

Jeannine Davis-Kimball, an expert on Eurasian nomads, was the first Westerner to see them and detail them in scientific journals. Nevertheless they remain little known. One of her descriptions of the tableau is featured on the website of the Center for the Study of Eurasian Nomads, where she is currently executive director.

The Kangjiashimenji Petroglyphs are carved in bas-relief in a sheltered grotto, at the base of a massive red-basalt outcrop in Tien Shan, about 45 miles west of Urumchi, the capital of Xinjiang province.

The cast of about 100 figures, which range in size from more than nine feet tall to just a few inches, are taking part in what is obviously a fertility ritual.

Almost all are depicted in the same ceremonial pose, in which their arms are held out and bent at the elbows with one hand pointing up and the other pointing down.