BISKUPIEC, Poland — During more than 10 years of tramping through fields and forests with a metal detector, a Polish treasure hunter has found the wreckage of an American-made Sherman tank, the scabbard of a French sword used by a soldier in Napoleon’s army, a Prussian helmet and many other relics of Europe’s bloody past.
In November, however, he made a discovery that has startled even scholars steeped in the ebb and flow of European warfare and left them wrestling with a tantalizing question: How did a cornfield in northeastern Poland come to hold silver coins minted more than 1,100 years ago and nearly 1,000 miles away by the medieval rulers of what is now France?
One theory, promoted by a Polish archaeologist leading the hunt for an explanation, is that the silver coins date from one of Europe’s earliest and most traumatic episodes of armed extortion — when an invading Viking army laid siege to Paris in 845, and had to be paid off with more than two tons of silver to prevent it from destroying the city.
The Vikings — Scandinavian warriors greatly feared because of their unruly habits and military prowess — later systematized what became an elaborate protection racket in the 11th century by imposing taxes in England known as Danegeld, tribute payments in return for safety.
What happened to the huge ransom they received for sparing Paris in 845, however, has always been a mystery.
The Vikings had a major trading post called Truso just 30 miles from Biskupiec, the Polish village where the coins were found. That has led some experts to speculate that the silver extorted in Paris made its way there and then spread into nearby areas as part of a flourishing Baltic-region trade, whose main commodity was slaves.
“This is an exceedingly rare and surprising find,” said Lukasz Szczepanski, the head of archaeology at a regional history museum in the Polish town of Ostroda. “We previously only knew what happened in Paris from written sources, but now, suddenly, we have it in a physical form.”
Others are skeptical. Simon Coupland, a British expert, noted that the coins found in Biskupiec seemed to date from several years before the 845 siege.
But, he added, they could be part of the booty extracted by the Vikings during earlier attacks on the western part of the empire established by Charlemagne, or simply the proceeds of regular trading and raiding by the Vikings.
Mr. Szczepanski acknowledged that his theory that the coins were part of the ransom the Vikings extorted to spare Paris was merely a “working hypothesis.”
A clearer picture, he said, would emerge after a chemical analysis of the coins and a full excavation of the site where they were discovered by the local treasure hunter, Przemyslaw Witkowski, and a fellow scavenger, Maciej Malewicz.
But, no matter what, Mr. Szczepanski said, the discovery of silver coins in a Polish hamlet from so far away and so long ago was both exciting and unsettling.
In a country whose own capital, Warsaw, was occupied and then obliterated by the Nazis during World War II, the survival of Paris more than a millennium before thanks to a payment to the Vikings has a painful resonance.
Despite their reputation for violence, medieval Vikings, Mr. Szczepanski said, behaved far better than 20th-century Germans, whose actions during the war “are incomparable with anything in world history.”
The trauma of World War II, he added, has severely hampered archaeological work in northern Poland. Much of the area used to be part of Germany, and postwar Polish archaeologists, focused on uncovering and celebrating their battered country’s own past, have had little interest in digging up reminders of German hegemony.
Tipped off by Mr. Witkowski about the November find in the cornfield, Mr. Szczepanski joined forces in March with amateur treasure hunters. Using metal detectors, they uncovered more than 100 more silver coins minted during the Carolingian Empire, which was founded in the early ninth century by Emperor Charlemagne. His empire once covered most of the territory that today makes up France, Italy and Germany.
Mr. Szczepanski is now making plans for a full-scale excavation of the field this year, once the farmer who owns the land finishes harvesting his crops. The discovery of yet more Carolingian coins, the archaeologist said, would strengthen his belief that the area contains part of the vast horde of silver paid to the Vikings.
All but one of the coins found so far date from the rule of Louis the Pious, Charlemagne’s son, with the rest minted under his grandson Charles the Bald, who ruled the western part of the Carolingian Empire and was in power during the Viking siege of Paris.
This, according to Stéphane Lebecq, an emeritus professor at the University of Lille in France and a leading expert in French medieval history, suggests that the stash had been “collected together at the beginning of Charles’s reign, so around 840-850, in the heart of his kingdom, which was situated in the Paris basin.”
So far, however, archaeologists have found only coins, not any of the silver ingots that almost certainly featured in the payment extorted by the Vikings from Charles the Bald. The discovery of ingots, Professor Lebecq said, would strengthen the ransom theory.
The silver coins so far uncovered, many of them intact but others smashed — apparently by the farmer’s plow — have been sent to Warsaw to be analyzed by experts at an archaeology laboratory run by the Polish Academy of Sciences.
Mateusz Bogucki, the head of the laboratory, said he was skeptical about the Paris ransom payment theory but said the coins were still a very significant find, indicating the reach of the Carolingian Empire far beyond its heartland in Western Europe.
The coins, he said, have little financial value and would most likely fetch under $200 each on the open market, “but their value as a source of information is absolutely amazing.”
Particularly important, Mr. Bogucki said, is the light they shed on medieval trade routes, many of which revolved around the buying and selling of local people who had been captured in battle and sold or forced into bondage by slave merchants.
The Vikings played a major role as intermediaries in a brutal business fed by a voracious appetite for slaves from Europe among wealthy Muslims in the Middle East and later Central Asia. Silver coins found previously in the area have mostly been Arab dirhams, used by Muslim merchants to pay for human chattel.
Mr. Witkowski, the treasure hunter, said he had initially paid little attention to his find because buried coins are often just an annoyance — usually dropped Polish zlotys.
“I generally don’t like coins,” he said.
But, after washing his find at home and realizing it was not just ordinary pocket change, he sent photographs to Mr. Szczepanski at the history museum in Ostroda. The archaeologist quickly called back and “was so excited I could not understand what he was saying,” Mr. Witkowski recalled.
“I realized that I had found something important,” he added.
Fearful that unscrupulous treasure hunters will start searching for and stealing the silver coins, the authorities have now sealed off the site near Biskupiec and declared its exact location a state secret.
At the same time, they recently rejected Mr. Witkowski’s application for a search permit, complaining that maps he submitted detailing the areas he and his associates would like to search were in the wrong format.
“There would be a lot more stuff in our museums if they did not make everything so complicated,” Mr. Witkowski said. Except for the archaeologist at the history museum, he added, “nobody has even said thank you for finding these coins.”