Did you know that the vikings served as a sort of imperial army and even as palace guards for the Byzantine emperors: The good news is that the socalled "anonymous folles" are actually easily collectable for only about 10-20 euro or dollars as the Byzantines struck, struck and struck so many of them in a golden period. And what an amazing piece of history you have in hand in a very important period in European and Byzantine history. The vikings 100% definitely would have known those above. You bought food with them, and Byzantines had a monetary economy where bronze coins circulated in the empire.
I know they had a base of operations in Sicily but I didn't know they made it as far to Constantinople.
There's actually some runic graffiti in Hagia Sophia! Maybe they were engraved by members of the Varangian Guard, or just by some wayward vikings who found themselves in Constantinople...
