A damaged gold plaque showing two birds of prey gripping a fish was part Britain's largest haul of Anglo-Saxon treasure, which was discovered buried in a Staffordshire field. (Eddie Keogh/Reuters)

An amateur treasure hunter prowling English farmland with a metal detector stumbled upon the largest Anglo-Saxon find ever, a massive seventh-century hoard of gold and silver sword decorations, crosses and other items, British archeologists said Thursday.

One expert said the treasure would revolutionize understanding of the Anglo-Saxons, a Germanic people who ruled England from the fifth century until the Norman conquest in 1066. Another said the find would rank among Britain's best-known historic treasures.

"This is just a fantastic find completely out of the blue," Roger Bland, who managed the cache's excavation, said. "It will make us rethink the Dark Ages."

Bland said the hoard was unearthed in what was once Mercia, one of five main Anglo-Saxon kingdoms, and is thought to date to 675-725 AD.

A total of 1,345 items have been examined by experts and 56 more lumps of earth have been found to contain metal artifacts detected by an X-ray machine, meaning the total will likely rise to about 1,500.

"I think wealth of this kind must have belonged to a king, but we cannot say that for absolute certain," Bland said.

The Anglo-Saxons were a group of Germanic tribes who gradually invaded England by sea starting in the fifth century in the wake of the collapse of the western part of the Roman Empire. Originally, they came from what is now the coastal region of northwest Germany.

Their artisans made striking objects out of gold and enamel and they also created poetry that still amazes people today. Their best-known literary work is Beowulf, an anonymous epic poem about a warrior who does battle with monsters and a dragon.

Leslie Webster, the former curator of Anglo-Saxon archeology at the British Museum, said the amount of gold uncovered — about five kilograms — suggested that early medieval England was a far wealthier place than previously believed.

The seventh-century hoard found by 55-year-old Terry Herbert in western England consists of at least 650 items of gold and 530 silver objects weighing more than a kilogram, along with some copper alloy, garnets and glass.

Most of the objects are ornaments for weapons and other military artifacts, some inlaid with precious stones.

'In my sleep I was seeing gold'

Herbert, from the town of Burntwood, found the gold on a friend's farm on July 5 and spent the next five days scouring the field for the rest of the hoard.

Herbert recovered the first items before professional archeologists took over the excavation.

"Imagine you're at home and somebody keeps putting money through your letterbox. That was what it was like," Herbert said. "I was going to bed and in my sleep I was seeing gold items."

The hoard was officially declared treasure by a coroner, which means it will now be valued by a committee of experts and offered up for sale to a museum. Proceeds would be split 50-50 between Herbert and his farmer friend, who has not been identified. The find's exact location is being kept secret to deter looters.

Bland said he could not give a precise figure for the worth of the hoard, but he said the treasure hunter could be in line for a "seven-figure sum."

Herbert said the experience was "more fun than winning the lottery," adding that one expert likened his discovery to finding Tutankhamen's tomb.

The hoard is in storage at the Birmingham Museum and Art Gallery. Some of the items are due to go on display starting Friday.

Bland said archeologists are still baffled by the function of many of the pieces they found.

"There's lots of mystery in it," he said.