research suggests that one of the most tranquil market towns in the region was once an unlikely cradle of military technology.

Best-selling writer Bill Bryson yesterday unveiled visitor facilities that give an insight into the brutal past of Helmsley, on the edge of the North York Moors.

The US author, an ardent anglophile who is now an English Heritage commissioner, opened the £900,000 centre at the town's 800-year-old castle.

Among the scores of previously unseen relics on display are arrowheads that have shed new light on the town's past.

The armour piercing arrowheads, which were strengthened with copper alloy, are believed to be the only ones ever found at an English castle.

The Royal Armouries, in Leeds, has confirmed similar arrows have been found in the wreckage of the Mary Rose.

They represented the ultimate advance in arrow technology at the time.

The arrowheads were dug from the ground in Helmsley in the 1920s.

Ever since then they have been kept under lock and key in stores at York.

Made in the 15th Century, they are capable of splitting open chain mail and armour with lethal results.

English Heritage senior curator Andrew Morrison said: "It seems that arrow technology may have reached its peak in Helmsley, before the advent of firearms.

"In a linked discovery we have also confirmed through the analysis of slag that the castle had its own ironworker and forge. Amazingly, it's the first definite evidence for smithying at any castle in the country.

"The iron working was almost certainly linked in some way to the monks at nearby Rievaulx Abbey, who came close to producing a primitive form of blast furnace."

The visitor centre was created by English Heritage in partnership with regional development agency Yorkshire Forward and with European financial support.

After trying his luck with a bow and arrow, Mr Bryson said: "I hope this centre gives the castle more of the public profile that it deserves."

Helmsley has the most extensive and best preserved collection of relics at any northern English castle.

It attracts 25,000 visitors a year, which is expected to increase to 45,000, providing a £2m lift to the local economy.