Calamity after calamity befell Europe at the beginning of the so-called Dark Ages. The Roman Empire collapsed in the late fifth century. Volcanic eruptions in the mid-sixth century blocked out the sun, causing crop failure and famine across the Northern Hemisphere. Meanwhile, the Justinian Plague arrived, killing, by some estimates, nearly half of everybody in Constantinople, the capital of the Byzantine Empire, and scores of others elsewhere.

And then, on June 8, 793, a group of marauders attacked a small island off the northeastern coast of Great Britain. As Christian monks noted in the Anglo-Saxon Chronicle, “heathen men destroyed God’s church in Lindisfarne island by fierce robbery and slaughter.”

With that description, the Vikings entered the annals of medieval history as merciless raiders, having also killed a local official in southern Great Britain in 789. From today’s perspective, these Norse seafarers burst into existence seemingly out of nowhere. Exactly when and why the Vikings first turned their boats away from shore to sail south over the horizon and into the unknown is hotly debated. According to some historians, another development in the late eighth century offers a clue: Silver coins known as dirhams made their way to Europe from the Islamic world in the Middle East. Around this time, Viking men in what is now Norway and Sweden became obsessed with silver as a means to purchase brides made scarce by female infanticide, or so a popular theory holds. A desperate need for silver, it was thought, motivated the Vikings’ initial trips across the North and Baltic seas and somehow precipitated their infamous raids.

Other historians, however, suspect the Vikings’ first forays into the outside world long preceded their violent raids and had nothing to do with a quest for silver. “Our understanding of the chronology of the early Viking Age is really patchy because our best accounts are sometimes written 100 years later,” says Matthew Delvaux, a medieval historian at Princeton University. That includes the description of the Lindisfarne raid in the Anglo-Saxon Chronicle.

Fortunately, medieval scholars have recently found another aid to turn to: a solar storm. Archaeologist Søren Sindbæk and his colleagues at Aarhus University in Denmark have reconstructed the timing of the Vikings’ early voyages by harnessing the power of what was likely a supermassive solar flare that erupted in 775. The flare has helped the team improve radiocarbon dating and thus more precisely date artifacts excavated at Ribe, Denmark, the site of an early medieval trading post.

The chronology of events at Ribe reveals a less violent start for Viking voyages, at least 50 years before the Lindisfarne raid. The secret of Viking success, Sindbæk believes, is best explained by skillful trading, not fearsome raiding.