Editor’s Note: This article was adapted from its original form and updated to include new information for Smithsonian’s Mysteries of the Ancient World bookazine published in Fall 2009.

From his bench toward the stern of the Sea Stallion from Glendalough, Erik Nielsen could see his crewmates’ stricken faces peering out of bright-red survival suits. A few feet behind him, the leather straps holding the ship’s rudder to its side had snapped. The 98-foot vessel, a nearly $2.5 million replica of a thousand-year-old Viking ship, was rolling helplessly atop waves 15 feet high.

With the wind gusting past 50 miles an hour and the Irish Sea just inches from the gunwales, “I thought we’d be in the drink for sure,” says Nielsen, now 63, a retired Toronto geologist.

It was August 6, 2007, and the Sea Stallion’s crew of 63 had been underway for five weeks, sailing from Roskilde, Denmark, to Dublin, Ireland, on a voyage that would culminate 35 years’ research—“the best living-archaeology experiment ever conducted anywhere,” Pat Wallace, director of the National Museum of Ireland, calls it.

As Nielsen and some of his crewmates struggled to keep the Sea Stallion upright, four others went to work at the stern. Kneeling on the ship’s heaving, rain-slicked deck, they hauled the 11-foot rudder out of the water, replaced the broken leather straps with jury-rigged nylon ones and reattached the new assembly.

Reducing the sail to a minimum, the crew proceeded at nine knots. As the ship plowed from wave to wave, a full third of the Sea Stallion’s hull was often out of the water. Ahead lay the Isle of Man, 15 hours away.

Two weeks later, its crew exhausted, the Sea Stallion limped into the port of Dublin for a nine-month refurbishment in dry dock at the National Museum of Ireland. In July 2008, it sailed, relatively uneventfully, back to Denmark. Ever since, researchers have been poring over reams of data from both voyages, gathered from electronic sensors on the ship, to learn more about the Vikings’ sailing prowess. Their findings will follow a host of recent discoveries by historians, archaeologists and even biologists that have led to a new understanding of the Vikings as a people who were as adept at trading as they were at raiding.

Norsemen have been seen as intrepid seafarers and fierce warriors—a sort of Hell’s Angels of the early Middle Ages—since A.D. 793, when they raided the rich island monastery at Lindisfarne off the northeastern coast of England. “The ravages of heathen men miserably destroyed God’s church on Lindisfarne,” according to the annals known as the Anglo-Saxon Chronicle. In 845, the Viking raider and extortionist extraordinary Ragnar Lothbrok slipped up the Seine with 120 ships—an estimated 5,000 men—to Paris, where King Charles the Bald paid him 7,000 pounds of gold and silver to leave in peace. (A contemporary wrote that “never had [Ragnar] seen, he said, lands so fertile and so rich, nor ever a people so cowardly.”)

Viking raiders traveled thousands of miles to the east and south: across the Baltic, onto the rivers of modern-day Russia and across the Black Sea to menace Constantinople in 941. “Nobody imagines they were there to capture the city,” says Cambridge University historian Simon Franklin. “It was more terroristic—all about instilling fear and extracting concessions for trade.”

At the same time, the new research suggests that the Vikings pouring out of Denmark, Sweden and Norway 1,200 years ago had more than raiding on their minds. Buying and selling goods from places as distant as China and Afghanistan, they also wove a network of trade and exploration from Russia to Turkey to Canada. “They were people without boundaries,” says Wladyslaw Duczko, an archaeologist at the Institute of Anthropology and Archaeology in Pultusk, Poland. “I think that’s why Vikings are so popular in America.”

Recent climate research has led Duczko and others to posit that a warming trend around the ninth century led to a population boom in Scandinavia, causing more and more landless young Norsemen to seek their fortunes elsewhere. Not everyone agrees. The National Museum of Ireland’s Wallace says the Vikings may have had a simpler motive: “They had the best iron in the world, trees to cut down and build ships, the best swords and edges on their blades. All the factors were there. They could do it, and they did.”

Whatever the causes for the Vikings’ explorations, evidence of the range of their trading networks began turning up about 150 years ago, when their elaborate burial mounds were first excavated. Well-preserved graves in Birka, Sweden, for example, contained fragments of Chinese silk, and in Norway, the ships in which wealthy Vikings were customarily buried were painted with pigments that may have come from India and the Middle East.

In the 1970s, archaeologists in Dublin found a Viking settlement spread over several acres—and in it more than 3,000 pieces of amber that were probably imported from Denmark. Excavation at Staraya Ladoga, outside St. Petersburg, unearthed a multiethnic settlement that included Viking jewelry, weapons and tools buried amid 1,000-year-old houses. And elsewhere in Russia, archaeologists have uncovered hundreds of Scandinavian graves containing artifacts from the Viking era; in 2006, they found one in the province of Kaliningrad, 500 miles from Norway.

Almost all these sites share a common artifact: thin, silver coins called dirhams. Most of them were made in Baghdad, which was the center of the Arab world from 750 to 950, and they were usually stamped with the year they were minted. Vikings apparently traded furs, amber, ivory and slaves for dirhams, which they then carried with them on their ships. As a result, the coins mark Viking trade routes like shiny silver bread crumbs.

In January 2007, metal-detector hobbyists in Harrogate, England, uncovered a treasure worth millions of dollars that one or more Vikings buried around 927; it included 617 coins, 15 of which were dirhams. Thousands of dirhams dating from 780 to 1050 were found at Viking sites near St. Petersburg. In Poland, archaeologists excavating a Viking settlement near Gdansk found nearly 800 coins dating from 780 to 840, almost all of them Arabic. Other Arabic coins made their way to France, Ireland, Iceland and Greenland. “What we’re seeing is the remnants of an extremely intricate network of barter trade,” says historian Jonathan Shepard of St. Kliment Ohrid University in Sofia, Bulgaria. “It’s a weird combination of coercion and tribute side by side and intermingled with bartering.”

By the 11th century, Vikings began adopting the languages and customs of local peoples, even settling in and intermarrying from Ireland to Russia. Researchers at the universities of Leicester and Nottingham, in England, found that up to half the DNA from men in northwest England matches Scandinavian genetic types.

All that wandering would have been impossible without ships—which is where Erik Nielsen and the rest of the Sea Stallion’s crew come in. For much of the 20th century, archaeologists assumed that Viking ships all resembled a vessel excavated in Norway in 1880. Known as the Gokstad ship, for the farm on which it was found, it dated to the year 900. The ship was “clinker-built,” meaning it was constructed of overlapping planks, which made it stout, flexible and light, with a sail and room for 32 oarsmen. In 1893, Magnus Andersen sailed a replica from Norway to Chicago for the World’s Fair. “Gokstad was thought to be universal, whether trader or raider,” says Niels Lund, a Viking historian at the University of Copenhagen. But a 1962 discovery forced researchers to abandon the idea that the Vikings had only one kind of ship.

At the bottom of a fjord near Roskilde, archaeologists found remnants of five Viking ships piled one atop the other. Dubbed the Skuldelev ships, for a nearby town, each had had a specialized role. One had been a fishing boat; two were cargo ships, so easy to handle that a crew of eight or nine could move 20-ton loads; and one was a warship that could carry about 30 people. The fifth ship, a raider named the Skuldelev, was the largest.

It was 98 feet long but just 12 feet wide. Its keel reached just three feet below the surface, and its masts and sail could be lowered so the ship could approach fortifications and settlements with stealth. It could accommodate 65 armed men. “This is a boat for warriors,” says Soren Nielsen, head boat builder at the Viking Ship Museum in Roskilde.

Because only about 20 percent of the Skuldelev 2 could be recovered, the only way to determine its capabilities for certain was to reconstruct it and put it to sea. In 2000, Nielsen and his colleagues at the ship museum began working with scientists to build an accurate replica. They used thousand-year-old methods and reproductions of tools from that time, which meant carving each of the ship’s 90 oak planks with axes, wedges and hammers. After four years and almost $2.5 million, the eight builders had their replica. They called it Sea Stallion From Glendalough for the Irish village where Vikings used to procure oak for their ships. With its narrow beam and shallow draft, the Sea Stallion could navigate just about any river in Europe. But how would it fare on the open sea?

In the summer of 2006, the Sea Stallion sailed under sunny skies and gentle winds to Norway and back in four weeks—a virtual pleasure cruise. A test sail in May 2007 around the Roskilde Fjord enjoyed similar conditions. “We like to say we’ve been cursed with good weather,” said Carsten Hvid, the Sea Stallion’s skipper. But the six-week voyage that began in July 2007— from Roskilde north to Norway, west to Scotland and south to Dublin—proved a tougher test. Fully loaded, the ship weighed 24 tons—eight of ship, eight of rock for ballast and eight of crew and gear. In ideal conditions, the Sea Stallion could travel 160 nautical miles in a day; it could sprint at 13 knots, or almost 15 miles an hour. (A high-tech America’s Cup racer might hit 20 knots.) “It ranks as one of the fastest warships in history,” says Anton Englert, an archaeologist at the ship museum.

For the July 2007 voyage, the ship set sail under dark skies that presaged Northern Europe’s coldest and wettest summer in decades. Nighttime temperatures plunged into the 30s. Three days into the voyage, two crew members had to be treated for hypothermia, and, to stay on schedule, Hvid had to accept a 24-hour tow across part of the North Sea because of weak winds. “It kept on raining and raining and raining,” says crew member Henrik Kastoft, in his day job a spokesman for the United Nations Development Program. “There were so many nights I just sat there shivering for hours.” Each crew member had about eight square feet of space. “I really suffered from being so close to people for so long. I got edgy, cranky,” says Erik Nielsen. “Maybe the modern analogue would be a submarine.”

If the night the rudder broke was the low point of the voyage, sailing along the western coast of Scotland almost made up for it. For nearly two weeks, the crew had the dramatic scenery almost completely to themselves. As the ship neared Dublin, escorts appeared. When it cruised up the River Liffey into port on August 14, ships and cars blasted their horns, church bells pealed and throngs of people waved from the balconies and windows of riverfront buildings.

Days later, the ship was trucked to the center of Dublin and lifted by a crane over a four-story building into the courtyard of the National Museum of Ireland, where it would spend the winter. By then, archaeologists at the ship museum in Roskilde had begun analyzing data generated during the voyage. As the crew’s close call in the Irish Sea made clear, high speeds over long distances pushed the ship to its limits—and challenged assumptions about how the original had been put together. “The sails are very stable and can take a lot of wind, but the problems with the rudder come up again and again, and haven’t been solved yet,” Englert says.

Information from the crew proved as valuable as technical data. Exhausted sailors told researchers that the close quarters made sleeping nearly impossible. Between the rough water, constant rain and their nautical duties, it was all crew members could do to nap for an hour or two during their rest periods. “That indicates the ship must have had an amphibious behavior—they had to land often just to get some rest,” Englert says. Crossing the North Sea in a narrow ship like this one would have stretched a Viking crew almost to the breaking point, and crossing the Atlantic would have been inconceivable. A ship like this would have likely been used for coastal raiding only.

On June 29, 2008, the Sea Stallion sailed once again, down the Liffey and out of Dublin harbor. It was, crew member Louise Kaempe Henriksen would blog, “typical Sea Stallion weather—pouring rain.” The ship set course south and then east around England to the cliffs of Dover, north to Lowestoft, then across the North Sea, following its Viking predecessors northeast toward home.

At last, after 1,261 nautical miles, the Sea Stallion reached Denmark a little more than a month later, on August 9. “We turn to Roskilde,” wrote crew member Vibeke Bischoff as they neared port. “We are escorted the whole way in,” he reported of their festive homecoming, “by hundreds of boats.” History does not record whether the Vikings, more than a millennium ago, were similarly greeted by their own vessels, bearing tidings of welcome to seafarers who were at last nearing landfall.