ONE of the biggest ancient hillforts ever found in Britain has been unearthed by archaeologists at a North Yorkshire beauty spot.

The 40-acre monument at Sutton Bank, near Thirsk, is thought to have been surrounded by a 1.3 mile-long rampart, topped with a walkway, and to date back to about 400BC.

The fort, which was built against a steep escarpment giving it views for miles across the Vale of York, was discovered by English Heritage archaeologists who spent this summer surveying the site.

Field investigator Alastair Oswald said there had been suspicions of an ancient hill fort at the location since the last century when a small number of Iron Age earthworks were discovered.

But Mr Oswald said the breathtaking array of ditches, humps, banks and others features - some of which are three metres high - was much more extensive than anyone had thought. He said: "Hillforts are uncommon in Yorkshire, so we were obviously shocked to discover such a huge complex.

"Over the years, there have been tantalising clues that such a monument existed, but no one had done a comprehensive survey to settle the question.

"It's possible the fort was constructed by the Brigantes or Parisi tribes, perhaps more as a statement of power than a defensive bastion."

Mr Oswald said the fort was enclosed by a two-metre deep trench and a four-metre high "box rampart", which would have been fronted by timber and have had a walkway along the top. He said it could have been used as a temporary refuge or for keeping livestock safe.

"What is certain is that such a large fort would have taken a vast amount of timber and labour to build which poses many more intriguing questions."

The North York Moors National Park Authority is now looking at how to present the find to visitors, including walkers on the nearby Cleveland Way.

Updated: 11:07 Thursday, November 08, 2001