According to historians, the Viking Age began on June 8, A.D. 793, at an island monastery off the coast of northern England. A contemporary chronicle recorded the moment with a brief entry: “The ravages of heathen men miserably destroyed God’s church on Lindisfarne, with plunder and slaughter.” The “heathen men” were Vikings, fierce warriors who sailed from Scandinavia and bore down on their prey in Europe and beyond in sleek, fast-sailing ships. In the centuries that followed, the Vikings’ vessels carried them deep into Russia and as far south as Constantinople, Sicily, and possibly even North Africa. They organized flotillas capable of carrying warriors across vast distances, and terrorized the English, Irish, and French coasts with lightning-fast raids. Exploratory voyages to the west took them all the way to North America.

The Vikings’ explosion across Europe and Asia and into the Americas was the result of the right combination of tools, technology, adventurousness, and ferocity. They came to be known as an unstoppable force capable of raiding and trading on four continents, yet our understanding of what led up to that June day on Lindisfarne is surprisingly shaky. A recent discovery on a remote Baltic island is beginning to change that. Two ships filled with slain warriors uncovered on the Estonian island of Saaremaa may help archaeologists and historians understand how the Vikings’ warships evolved from short-range, rowed craft to sailing ships; where the first warriors came from; and how their battle tactics developed. “We all agree these burials are Scandinavian in origin,” says Marge Konsa, an archaeologist at the University of Tartu. “This is our first taste of the Viking era.”

Between them, the two boats contain the remains of dozens of men. Seven lay haphazardly in the smaller of the two boats, which was found first. Nearby, in the larger vessel, 33 men were buried in a neat pile, stacked like wood, together with their weapons and animals. The site seems to be a hastily arranged mass grave, the final resting place for Scandinavian warriors killed in an ill-fated raid on Saaremaa, or perhaps waylaid on a remote beach by rivals. The archaeologists believe the men died in a battle some time between 700 and 750, perhaps almost as much as a century before the Viking Age officially began. This was an era scholars call the Vendel period, a transitional time not previously known for far-reaching voyages—or even for sails. The two boats themselves bear witness to the tremendous technological transformations in the eighth-century Baltic.

In 2008, workers digging trenches for electrical cables in the tiny island town of Salme uncovered human bones and a variety of odd objects that they unceremoniously piled next to their trench. Local authorities at first assumed the remains belonged to a luckless WWII soldier, until Konsa arrived and recognized a spearhead and carved-bone gaming pieces among the artifacts, clear signs the remains belonged to someone from a much earlier conflict. Together with a small team, Konsa dug a little deeper and soon found traces of a boat’s hull. Nearly all of the craft’s timber had rotted away, leaving behind only discolorations in the soil. But 275 of the iron rivets holding the boat together remained in place, allowing the researchers to reconstruct the outlines of the 38-foot-long craft.

Soon Konsa realized she had found something unique for this place and period. “This isn’t a fishing boat, it’s a war boat,” Konsa says. “It’s quite fast and narrow, and also quite light.” Based on radiocarbon dating of tiny fragments of boat timbers, Konsa estimates the vessel was built between 650 and 700, and perhaps repaired and patched for decades before making its final voyage. It had no sail, and would have been rowed for short stretches along the Baltic coast, or between islands to make the journey from Scandinavia to the seafarers’ hunting grounds farther east. From bones found inside the boat, Konsa pieced together the remains of the seven men, all between the ages of 18 and 45. She also found knives, whetstones, and a bone comb among the remains. The craft was a remarkable find—the first such boat ever recovered in Estonia, complete with the bodies of its slain crew.

Two years later, Jüri Peets, an archaeologist at the University of Tallinn, uncovered evidence of another, far larger and more technologically sophisticated craft just 100 feet away from the first boat. Soon workmen were ripping up a nearby road to reveal the vessel they dubbed Salme 2—the smaller boat would later be called Salme 1. The Vikings’ tremendous geographic reach, from Nova Scotia to Constantinople, was made possible by their mastery of the ocean, particularly the sail. However, archaeologically speaking, there’s not a great deal of evidence for sailing in the Baltic until roughly 820, when researchers think a 60-foot-long vessel, called the Oseberg ship, was built. Discovered in 1904, the Oseberg ship was used for the burial of a high-ranking Viking woman in what is today Norway.

The Salme site may change all that, pushing the first evidence for sailing back a century or more. Though, again, most of the wood had disappeared, by measuring the position of the more than 1,200 nails and rivets and carefully looking at soil where the wood had rotted, Peets concluded that Salme 2 was about 55 feet long and 10 feet wide. The craft had a keel, an element critical to keeping a sailing ship upright in the water. Peets believes clusters of iron and wood near the center of the boat and pieces of cloth recovered from the soil are indications of a mast and sail.

If he is right, Salme 2 is the oldest sailing vessel ever found in the Baltic. And other scholars are inclined to agree. “I would think that the big Salme boat would be the perfect place to find the first example of a sail before the Viking Age,” says Jan Bill, an archaeologist and specialist in Viking ships at the University of Oslo. “It’s the size of vessel,” says Bill, “where a sail would make a lot of sense.” Salme 2, built, sailed, and beached a half-century or more before the first raids on England heralded the dawn of the Viking Age, was, for all intents and purposes, a Viking ship. The Salme 2 vessel was certainly capable of crossing the open sea between the Swedish coast and Saaremaa, a distance of about 100 miles. The vessel also shows that the key technology of the Viking Age took shape at least decades, and maybe almost a whole century, before 793.

Like its nearby sister vessel, Salme 2 brought a crew with it when it was buried. “Three days after we started digging, a sword was discovered, and after some days skeletons in rows began to appear,” says Ragnar Saage, a graduate student who worked with Peets on the excavation. It took two summers of painstaking work to excavate all the bodies: 33 in all, stacked neatly four deep. “We couldn’t believe our eyes,” says Saage. “It was a strange feeling to dig this kind of site.”

Taken together, the two ships represent a tantalizing mystery. Peets and Konsa agree the vessels were probably buried at the same time, as part of the same event. Based on the boats’ construction and the artifacts and remains found inside, the archaeologists believe the dead men were Scandinavian, probably from what is today Sweden, 150 miles away across the Baltic Sea. But what were they doing in Estonia? And why didn’t they make it home?

Peets, who finished excavating the larger ship, Salme 2, in September 2012, has gathered enough information to sketch out what might have happened. Lured across the sea by booty, to collect tribute from the locals, or to settle a grudge, a mighty raiding party met a formidable foe on this isolated beach. After a struggle, one side’s survivors—there’s no way to tell if they were the winners or the losers—gathered the bodies together and ceremonially destroyed their fallen comrades’ swords by burning, and then bending or breaking them.

The surviving warriors then had enough time to pull at least two of their ships 70 yards up the gently sloping beach. The 33 men of Salme 2, all of whom were vigorous, healthy adult men of fighting age, were then buried inside. This was done with obvious care and respect. “The skeletons were covered with shields, like a blanket,” says Saage. (The 15 shields have long since rotted away, but their bronze bosses and fragments of their handles remain.) The men were buried with their belongings, including everything from weaponry to elk-horn combs, joints of sheep and cow, and even the remains of dogs and a hawk. “Every time I tried to clean the skeletons or bring up bodies, I found more artifacts and swords,” says Raili Allmae, the forensic anthropologist in charge of excavating the site’s human remains. Fragments of textile, perhaps bits of a sail used as a shroud to cover the pile of bodies before sand was laid on top, were also recovered from among the bones. The condition and placement of the warriors in the smaller ship are harder to explain. Konsa used a program designed to help reconstruct crime scenes to piece together the men’s original locations. Some had been slumped in pairs or alone and some were leaning up against the inside of the hull in a sitting position. And these men are much less richly equipped than those found nearby.

While boat burials are familiar from both written sagas and archaeological finds in England, Sweden, and Norway, both the Salme ship burials are exceptional. Boat graves were almost always solo affairs, with a king or lord buried alone under a large earthen mound that covered the entire vessel. And no boat graves had ever been found this far east. The Salme boats are evidence that these later practices probably evolved over centuries, another thread connecting the Vendel period to the Vikings. “These burials correspond to medieval written descriptions of how you would bury warriors who died abroad,” says Bill. “It’s extremely interesting to see something very similar taking place in the pre-Viking period. Perhaps it tells us where those stories are coming from.”

Yet to trained eyes the burials bore indications of a rush job. Only the bodies in each ship were covered with sand, perhaps to discourage scavenging animals from disturbing them. Men moving rocks with their hands and scooping sand with their helmets could have done the job in a few hours. “It is an amazing find,” says John Ljungkvist, an expert in Iron Age burials at Uppsala University in Sweden. “It seems like a post-battlefield burial, but carries a lot of elements of a boat burial. They don’t have the time or the logistics to do a regular boat burial, and instead have to make a mass grave.”

The job done, the two boats and their cargo of corpses were then abandoned on the beach. Peets and Konsa think a heavy fall or winter storm might have washed up enough sand and gravel to partially fill in and cover the crafts. Over the next 1,300 years, the area’s coastline receded, leaving the boat graves buried more than 200 yards from the sea and 12 feet above the waterline.

The bodies themselves are already proving a rich source of information, drawing clear connections between the Vendel era and the aggression that would soon emerge as a Viking hallmark. Given the Vikings’ bloodthirsty reputation, surprisingly little is known about warfare leading up to the Viking era. “A mass grave from this period is unique,” says Ljungkvist. “We don’t have physical evidence of warfare and raiding, so that is very special.” By looking at the bodies, archaeologists can tell a great deal about how they died and how such raiding parties might have been organized.

It’s a key question. Scholars have long debated why the Vikings expanded as rapidly and aggressively as they did—and why the Viking raids on western Europe didn’t happen earlier. The theories range from climate change, with a warm period in Europe around 800 creating overpopulation that forced young men to seek their fortune elsewhere, to a coincidence of greed, wanderlust, and the technology to make long-distance raids possible.

The Salme finds suggest that the historical view of the Viking Age as a sudden phenomenon needs a radical adjustment. It’s clear from the remains that Scandinavian princes were organizing war parties decades or more before the fateful 793 raid on Lindisfarne: Though the men were interred en masse, the Salme sailing party was far from egalitarian. The weapons paint a picture of warriors led by a rich warlord or chieftain and a handful of well-equipped lieutenants. Even the stack of bodies on Salme 2 was hierarchical. Five men with double-edged swords and elaborately decorated hilts were buried on top. At the bottom, the bodies were buried with simple, single-edged iron blades. “These were some noblemen with their retinue,” Peets says. “The more elaborate swords are clearly connected to people of higher status.” One of the uppermost skeletons even had an elaborately decorated walrus-ivory gaming piece—perhaps the “king”—in his mouth. A jeweled sword hilt, the finest of the 40 blades in the burial, was found nearby. It’s possible the men found in Salme 1 were from the bottom of the social ladder. Konsa thinks they may have been servants or lower-class “support staff,” and buried with less care, and fewer grave goods, far away from the warriors and aristocrats of Salme 2.

To find out who these men were and where they came from, archaeologists are looking at the skeletons themselves. Since Peets finished excavating Salme 2 in fall 2012, the remains of the slain warriors have come to rest at the University of Tallinn’s Institute of History, a centuries-old stone building on a narrow side street in the Estonian capital’s medieval center. Neatly arranged in dozens of white cardboard boxes, they line one wall of a lab on the institute’s top floor, accessible via a groaning, creaking Soviet-era elevator. Forensic anthropologist Allmae has spent the last two years trying to untangle the story of the yellowed bones she pulls from the boxes.

Allmae has ample reason to think the men were felled in a fierce battle. Lying on a steel lab table is a humerus, or upper arm bone. Lining it up against her own arm, she demonstrates how the man probably raised his right hand over his head to ward off sword blows—to no avail. Deep chop marks cut clean through the bone. Another warrior’s skull was cut straight through. “Somebody chopped off the top of his head,” Allmae says. “I also suppose it was done with a sword—two strokes.” Only five of the 40 skeletons have clear cut marks on their bones, which she says isn’t unusual for mass graves—there are lots of ways to die in battle, after all. “There were also arrowheads in the body or in the pelvic area that could have been deadly but not touched the bones,” Allmae adds. Bloody flesh wounds that didn’t connect with bone could also have felled the men without leaving a lasting trace.

Unlike many battlefield graves, and different from the treatment of the seven men found in the first ship, the Salme 2 bodies seem to have been laid to rest with some thought to the afterlife. The man with the severed arm was found with the rest of his limb carefully arranged in its proper place. Allmae’s analysis shows that this would have been an intimidating crew, especially in eighth-century Europe. The average height was 5’10”, and several of the men might have been well over six feet tall. Some of the bones bear signs of old wounds, suggesting these were veterans of more than one scrap. Based on the style of the swords, arrowheads, and other weapons, in addition to the objects found in the graves and especially the boats themselves, Peets and Konsa are already certain that the men were from Scandinavia. “These were very typical swords for Scandinavian warriors,” Peets says. More clues may come from the chemical composition of the bones. Allmae plans to use a technique called isotopic analysis that matches chemical signatures in the bones to trace elements in water to help pin down where the men might have grown up.

For all the information the team has gathered from the excavation, there are some questions the dead men simply can’t answer. It’s clear there was a battle, but who was fighting whom? A saga written in 1225 tells of a Swedish noble named Yngvar who met his end while raiding in Estonia around 600. “The men of Estland came down from the interior with a great army, and there was a battle; but the army of the country was so brave that the Swedes could not withstand them, and King Yngvar fell, and his people fled,” the saga reads. “He was buried close to the seashore under a mound in Estland; and after this defeat the Swedes returned home.” It’s tempting—but ultimately impossible—to tie the Salme boats to Yngvar’s legendary expedition. “We shouldn’t use historical material to put a story behind the archaeological finds,” Konsa warns. “It’s dangerous to look for Yngvar in the Salme boats, but Salme confirms that the events in the saga might have happened.”

Saaremaa would have been a strange place for a raid. As far as we know from historical sources, Viking raids were usually aimed at population centers or rich, isolated monasteries—high-value targets, in other words. Did these proto-Vikings have similar goals in sight? The Estonian team can’t say. Nothing of the kind is known from this part of Estonia. The 1,200-square-mile island of Saaremaa is better known for bitter tank battles between Soviet and German troops during WWII than for Vendel-era sword fights, and decades of excavations around the island have turned up little in the immediate vicinity of the burials. “Saaremaa’s a pretty big island, but we don’t have any known settlements or graves from the period in the vicinity of the boat finds,” Saage says. “The closest are about 12 miles away.”

If the battle was a raid on a village, or a military clash with locals, the visitors may have won a costly victory. “They must have had some control of the battleground—not necessarily won, but enough time to make the boat graves,” says Saage. But the fact that the dead men and their grave goods were left untouched long enough for storms to cover them with sand suggests the area was abandoned after the fight.

Perhaps the men were fighting other Scandinavians. Konsa found arrowheads where the outside of the smaller ship’s hull would have been, as though arrows were embedded in the wood. “Maybe the battle had already begun out at sea,” she says, before fighting continued on the beach. Could rival warlords have been duking it out on an isolated shore, carrying on a feud begun back home? Or was this the final resting place of the fabled Yngvar, brought low by fierce local fighters? We’ll never know the whole story. But the remains of these bold, unlucky adventurers are enough to sketch out a powerful scene of a voyage gone badly wrong, and a warlord slain while leading his men into battle on a far-off shore.

Andrew Curry is a contributing editor at ARCHAEOLOGY.