As a child, Klaus Schmidt used to grub around in caves in his native Germany in the hope of finding prehistoric paintings. Thirty years later, a member of the German Archaeological Institute, he found something infinitely more important: a temple complex almost twice as old as anything comparable on the planet.

"This place is a supernova," said Schmidt, standing under a lone tree on a windswept hilltop 35 miles north of Turkey's border with Syria. "Within a minute of first seeing it I knew I had two choices: go away and tell nobody, or spend the rest of my life working here."

Behind him are the first folds of the Anatolian plateau. Ahead, the Mesopotamian plain, like a dust-coloured sea, stretches south hundreds of miles. The stone circles of Gobekli Tepe are just in front, hidden under the brow of the hill.

Compared with Stonehenge, they are humble affairs. None of the circles excavated (four out of an estimated 20) are more than 30 metres across. T-shaped pillars like the rest, two five-metre stones tower at least a metre above their peers. What makes them remarkable are their carved reliefs of boars, foxes, lions, birds, snakes and scorpions, and their age. Dated at around 9,500BC, these stones are 5,500 years older than the first cities of Mesopotamia, and 7,000 years older than Stonehenge.

Never mind wheels or writing, the people who erected them did not even have pottery or domesticated wheat. They lived in villages. But they were hunters, not farmers.

"Everybody used to think only complex, hierarchical civilisations could build such monumental sites, and that they only came about with the invention of agriculture", said Ian Hodder, a Stanford University professor of anthropology who has directed digs at Catalhoyuk, Turkey's best known neolithic site, since 1993. "Gobekli changes everything. It's elaborate, it's complex and it is pre-agricultural. That alone makes the site one of the most important archaeological finds in a very long time."

With only a fraction of the site opened up after a decade of excavation, Gobekli Tepe's significance to the people who built it remains unclear. Some think it was the centre of a fertility rite, with the two tall stones at the centre of each circle representing a man and woman. It is a theory the tourist board in nearby Urfa has taken up with alacrity. Visit the Garden of Eden, its brochures trumpet; see Adam and Eve.

Schmidt is sceptical. He agrees Gobekli Tepe may well be "the last flowering of a semi-nomadic world that farming was just about to destroy", and points out that if it is in near perfect condition today, it is because those who built it buried it soon after under tons of soil, as though its wild animal-rich world had lost all meaning.

But the site is devoid of the fertility symbols found at other neolithic sites, and the T-shaped columns, while clearly semi-human, are sexless.

Gods

"I think here we are face to face with the earliest representation of gods," said Schmidt, patting one of the biggest stones. "They have no eyes, no mouths, no faces. But they have arms and they have hands. They are makers.

"In my opinion, the people who carved them were asking themselves the biggest questions of all. What is this universe? Why are we here?"

With no evidence of houses or graves near the stones, Schmidt believes the hilltop was a site of pilgrimage for communities within a radius of roughly a hundred miles. The tallest stones all face south-east, as if scanning plains that are scattered with contemporary sites in many ways no less remarkable than Gobekli Tepe.

Last year, for instance, French archaeologists working at Djade al-Mughara in northern Syria uncovered the oldest mural ever found. "Two square metres of geometric shapes, in red, black and white - like a Paul Klee painting", said Eric Coqueugniot, of the University of Lyon, who is leading the excavation.

Coqueugniot describes Schmidt's hypothesis that Gobekli Tepe was a meeting point for rituals as "tempting", given its spectacular position. But surveys of the region were still in their infancy. "Tomorrow, somebody might find somewhere even more dramatic."

Vecihi Ozkaya, the director of a dig at Kortiktepe, 120 miles east of Urfa, doubts the thousands of stone pots he has found since 2001 in hundreds of 11,500-year-old graves quite qualify as that. But his excitement fills his austere office at Dicle University in Diyarbakir.

"Look at this", he said, pointing at a photo of an exquisitely carved sculpture showing an animal, half-human, half-lion. "It's a sphinx, thousands of years before Egypt. South-eastern Turkey, northern Syria - this region saw the wedding night of our civilisation."