Vikings traveled everywhere, not only on northern seas, but also the Black Sea, the Marmara, the Aegean, and the Mediterranean. An ethnic group called the Rus, believed to be Norse who settled around the Black and Baltic Seas and merged with Slavic locals, created a culture now called the Kievan Rus. They were the first recruits for the Varangian Guard, after their Christianization.
Over time, Constantinople sent emissaries north seeking to hire more. In 1195, Alexios Angelos sent requests for 1000 warriors each from Denmark, Norway, and Sweden to help him overthrow the emperor, who was his brother, and make himself Emperor Alexios III.
Many Norse, mostly Swedes, made the trip south on their own, seeking employment in the lucrative business of guarding the Byzantine emperor in Miklagarðr, ("Great City"). The number of them—and the consequences of their absence—was sufficient to create new laws. Sweden forbade receiving an inheritance if you lived in Greece. Norway decreed that departing for Greece forfeited your place in line regarding inheritance. Clearly they were happy if citizens brought money back, but were against seeing wealth leave their country for southern climes.
The Christianization of Kievan Rus that brought them to the attention of Byzantium and made them the source of the first Varangians has been touched on before, as has been the person who brought it about, but he did more than that. Next time we look more closely at Vladimir I of Kyiv.