The epic voyages of the Vikings to the British Isles, Iceland, North America and points west tend to obscure the fact that the Scandinavian warriors also ventured far to the east across Europe and parts of Asia. While the Danes and Norwegians sailed west, Swedish fighters and traders traveled in the opposite direction, enticed initially by the high-quality silver coins minted by the Abbasid Caliphate that sprawled across the Middle East.

These Vikings who crossed the Baltic Sea and descended across Eastern Europe were branded “Rus”—possibly derived from “ruotsi,” a Finnish word for the Swedes meaning “a crew of oarsmen” and the term from which Russia receives its name. As the Rus migrated down the Dnieper and Volga Rivers, they established settlements along trade routes to the Black and Caspian Seas and conquered the native Slavic populations in present-day Russia, Belarus and Ukraine.

By the middle of the 9th century, Rus merchants turned up in Baghdad. The capital of the Abbasid Caliphate may have been the world’s largest city with a population of more than one million people, but it failed to capture the Viking imagination like Constantinople, the capital of the Byzantine Empire that was said to harbor even greater riches.

“Silk and gold are the big lures,” says John Haywood, who chronicled the exploits of the Scandinavian raiders on four continents in his book, Northmen: The Viking Saga AD 793-1241. “The Rus would have heard stories about the riches of Constantinople. The big attraction in trade was silk, which was a massively prestigious product for which they traded slaves, furs, beeswax and honey with the Byzantines. Constantinople was also one of the few places that still had gold coins, which were in short supply compared to the Roman period.”

Constantinople’s location on the shores of the Bosporus strait, which divided Europe from Asia, allowed it to become a prosperous crossroads of trade, the largest city in Europe and the richest city in the world. Great treasures necessitated stout defenses. The most-heavily fortified city in the world, Constantinople was encircled by a moat and three parallel walls. In addition, an iron chain that could be stretched across the mouth of the city’s harbor protected it from a naval assault.

It is not known when the Rus first reached Constantinople, but it was before 839 when Rus representatives arrived at the Frankish court as part of a Byzantine diplomatic mission. In June 860, the Rus launched a surprise attack on Constantinople at a time when the city was left largely undefended as Byzantine Emperor Michael III was off with his army fighting the Abbasid Caliphate in Asia Minor while the Byzantine navy was engaged with Arab pirates on the Mediterranean Sea.

In what the Greek patriarch Photius called “a thunderbolt from heaven,” the Rus plundered the suburbs of Constantinople and launched coastal raids around the Sea of Marmara in which they burned houses, churches and monasteries and slaughtered the patriarch’s servants. However, they never attempted to breach the city walls before suddenly departing in August. The Byzantines credited divine intervention, but the Rus likely departed to ensure they could arrive back home before winter set in.

A medieval Russian source details a second attack on Constantinople in 907 when a fleet of 2,000 ships encountered the iron chain blockading the harbor entrance. The resourceful Vikings responded by going amphibious, hauling their ships ashore, affixing wheels and dragging them overland before placing them back in the water on the other side of the chain before being repelled by the Byzantines. No Byzantine accounts of a Viking attack in 907 exist, however, and Haywood notes that the story could have been concocted as a way to explain a subsequent trade agreement between the Rus and the Byzantines.

In 941 the Rus launched a disastrous attack on Constantinople. With the Byzantine army and navy once again gone from the city, a fleet of 1,000 ships descended upon Constantinople only to be done in by 15 old dromons fitted with Greek Fire projectors that set the Viking ships ablaze. Weighed down by their armor, the Rus who avoided the flames by jumping into the sea sank to a watery demise. Others caught fire as they swam. When Byzantine reinforcements finally arrived, the Rus sailed for home.

A half-century later, the Vikings would be recruited to defend Constantinople instead of attacking it. When Byzantine Emperor Basil II faced an internal uprising in 987, Vladimir the Great gave him 6,000 Viking mercenaries known as Varangians to differentiate the native Scandinavians from the Rus who by the middle of the 10th century had assimilated with the native Slavs and lost their distinct identity. Impressed by the ferocity with which the Vikings battled the rebels, the emperor established the elite Varangian Guard to protect Constantinople and serve as his personal bodyguards. With no local ties or family connections that could divide their loyalties and an inability to speak the local language, the Varangians proved far less corruptible than Basil’s Greek guards.

“They were immensely well rewarded,” Haywood says of the Varangians. “They were given silk for everyday wear. If you are Scandinavian at that time, you are doing well if you have silk trim on your clothes. They get an enhanced share of the booty. It’s this trickle of well-to-do homecoming mercenaries that spreads this image of Constantinople as the promised land of fabulous wealth.”

The Varangian Guard fought in every major Byzantine campaign—from Sicily to the Holy Land—until Constantinople was captured by Crusaders in 1204. Visitors to one of the most famous sites in the city now known as Istanbul can see that the Vikings left their mark on Constantinople—literally. At least two runic inscriptions carved into the marble walls of the Hagia Sophia may have been engraved by members of the Varangian Guard.