AERIAL laser scanning to discover the archaeological secrets under an area of ancient woodland have revealed prehistoric farming on "an astonishing scale".

The discovery of large scale farming from before the Roman invasion in the South Downs National Park suggests a degree of civilisation closer to ancient Greece, Egypt or Rome than what is known of prehistoric Britain, archaeologists said.

"Lidar" surveying of a wider area of the national park has also unearthed a Roman road which has been speculated about for decades, experts said.

The relatively new technique involves an aircraft mounted laser beam to scan the ground and produce accurate 3D models of features which survive as earthworks or structures in open land or woodland.

For the "secrets of the High Woods" project it was used to examine the archaeology protected under woodlands which have stood for hundreds of years.

The project, supported by the Heritage Lottery Fund, looked at an area in West Sussex and East Hampshire, between Queen Elizabeth Country Park and the Arun river valley.

Images of land between Lamb Lea Woods and Charlton Forest showed that a field system which was already protected as a scheduled monument was just a small part of a vast and continuous swathe of later pre-historic cultivation extending under a now wooded area.

The Lidar surveying also revealed the route of a long-speculated about Roman road between Chichester and what is now Brighton.

The project has confirmed that Romans heading east would have left Chichester on Stane Street before branching east and following a straight course - as most Roman roads were - towards Arundel through Binstead Woods.

Helen Winton, aerial investigation manager at Government heritage agency Historic England, said: "The recognition of the 'missing link' in the Roman road west of Arundel, by Fiona Small at Historic England, was a highlight in a project full of exciting results."

James Kenny, archaeological officer at Chichester District Council, said the evidence suggested the field system dates back to before the Romans settled in Britain.

It also raises many questions, as to who was growing the crops, who was eating the food and - given no settlements have been found - where were they living, he said.

"The scale is so large that it must have been managed, suggesting that this part of the country was being organised as a farming collective on a very large scale," he said.

"The degree of civilisation this implies is completely unexpected in this part of the world at this time - something closer to the Greeks, Romans and Egyptians than current views of pre-historic Britain."