Viking Hoard
©Bengt A Lundberg
A photo shows many of the 472 recently found silver coins that make up Sweden's earliest known Viking hoard. The cache of Middle Eastern coins suggests Vikings were trading extensively overseas earlier than previously believed.

Hundreds of ancient coins unearthed last week close to Sweden's main international airport suggests the Vikings were bringing home foreign currency earlier than previously thought, archaeologists say.

Buried some 1,150 years ago, the treasure trove is made up mainly of Arabic coins and represents the largest early Viking hoard ever discovered in Sweden.

Archaeologists from the Swedish National Heritage Board unexpectedly found the stash of 472 silver coins while excavating a Bronze Age tomb near Stockholm's Arlanda airport.

Kenneth Jonsson, a professor of coin studies at the University of Stockholm, has independently dated the hoard to about A.D. 850.

"That date is very early, because coin imports [by the Vikings] only start in about [A.D.] 800," Jonsson said.

The discovery contains more coins than Sweden's only other known large Viking hoard from the period, which was discovered in 1827, Jonsson added.

"That coins were so important to the Vikings at such an early date is very interesting" and suggests they may have engaged in intensive overseas trade earlier than previously believed, he said.

Viking Treasure

The newfound hoard consists only of eastern coins, which is unsurprising, since early Viking hoards are typically dominated by coins from the Middle East.

Most of the coins were minted in Arab locations such as Baghdad in modern-day Iraq and Damascus in Syria. The youngest coin dates to the A.D. 840s

But the oldest coins came from Persia, said dig team member Karin Beckman-Thoor.

These Persian coins must have been in circulation for centuries before being buried and "were very high quality," she said.

While Swedish Viking hoards are often found on the Baltic island of Gotland, they are much less common on the mainland.

Once thoroughly studied, the hoard "will give us lots of information about the journey it made and also ideas about why it was left in the ground," Beckman-Thoor said.

The Arlanda airport find might represent either loot from raids or profits from trade, she added.

Jonsson, of the University of Stockholm, favors the latter explanation.

"I think it's 95 percent trade," he said, adding that Vikings likely exchanged the coins for goods such as slaves, iron, tar, and amber.

While Vikings are documented to have traveled as far as the Middle East, most of this overseas trade probably took place in towns in Russia, a country rich in Viking remains, he said.

Most of the coins in the newfound hoard had been cut into pieces, Jonsson said, and the Vikings would have valued them principally for their 95 percent silver content.

"They put it on a scale and measured it and the weight gave the value of the silver," Jonsson explained. "They broke it into pieces to get exactly the amount of silver they needed."

Medieval Village

The stone burial chamber where the hoard was found is being excavated before a new housing development is constructed on the site.

Measuring 52 feet (16 meters) in diameter, the Bronze Age tomb is thought to be around a thousand years older than the buried silver.

Only a handful of Viking hoards have previously been discovered hidden within such prehistoric monuments.

It may be that the prominent burial stones were used as a landmark by Vikings who intended to come back for the silver, Beckman-Thoor said.

"Or perhaps they thought their ancestors would protect the hoard, or perhaps it was an offering for their ancestors," she said.

The site of a medieval settlement lies below the hill where the stone monument is located, Beckman-Thoor noted.

"We believe the village goes back to the Viking age," she said.