A Celtic treasure looted by the Vikings more than 1,000 years ago has been discovered in the storerooms of the British Museum in central London.

The ornate, gilded disc brooch, dating from the eighth or ninth centuries, is being described as a "staggering find." It had been concealed in a lump of organic material excavated from a Viking burial site at Lilleberge in Norway by a British archaeologist in the 1880s and acquired by the British Museum in 1891.

Curator Barry Ager, a Viking specialist, said the discovery "shows contact between the British Isles and Norway in the Viking period . . . objects seized as loot in this country and taken back." The brooch, almost 6 cm in diameter, had been buried in the grave of a high-status Viking woman. Substantial remains of the gilding still survive on the top surface, and its elaborate design includes three dolphinlike creatures and interlaced patterns.

A major exhibition, "Vikings: Life and Legend," which focuses on the core period of the Viking age from the late eighth century to the early 11th century, will include the remains of a 37-meter Viking longship — the longest ever found and never seen before in the U.K. — runs from March 6 to June 22.