An amateur archaeologist from Old Town, Swindon, believed he had stumbled across Swindon's answer to Stonehenge.

Former welder Ken Woolley couldn't believe his eyes when he saw a cluster of 6ft-tall stones on a building site in Savernake Street.

But the find dates back much further than Stonehenge and forces far greater than man are responsible.

In fact, the rocks are part of the Portland stone beds, formed millions of years ago.

Mr Woolley, 64, of Stafford Street, said: "I couldn't believe it when I looked outside my back window and saw the huge stones on the building site.

"They are much bigger than me. At first I thought they could be related to Stonehenge. The colours and shapes look quite similar.

"I have been on a lot of excavation sites with my building work but I've never seen stones like these before."

Mr Woolley's kitchen overlooks the building site, on which Old Town developers Hannick Homes are building 11 flats.

He called Swindon's top archaeologist Bryn Walters following the discovery at the weekend.

He said: "I was quite excited with the find and wanted to get an expert opinion as soon as possible, before the workmen broke them up.

"It would have been terrible if an ancient treasure was destroyed because no one had checked it."

Dr Walters, director of the Swindon-based Association for Roman Archaeology and a lecturer at Bath University, confirmed that the rocks were ancient.

He said: "The rocks are geologically, rather than archaeologically, interesting.

"They are from the Portland beds, which the Romans used to quarry for building and foundation work, so we don't see it very often.

"Old Town hill is geologically on an anticline. The Portland beds run down underneath the chalk of the Marlborough Downs. The main outcrop is at Portland, in Dorset.

"It breaks up at Swindon due to tectonic plate movements, which create folds in the rock formed many millions of years ago. A fault created Swindon hill."

Andrew Downton, construction director at Hannick Homes, confirmed building had started at the Savernake Street site.

He added: "The building will consist of 11 one and two-bedroom flats, with 11 parking bays, and is due for completion in November or December."