The first runic inscription was discovered in 1964 on a parapet on the top floor of the southern gallery, the inscription is worn down so only -alftan, which is the Norse name Halfdan, is legible.
A second inscription was discovered by Folke Högberg from Uppsala in 1975 in a niche in the western part of the same gallery and is considered by some experts to be Viking grafitti.
They may have been engraved by members of the Varangian Guard who were an elite unit of the Byzantine Army, from the 10th to the 14th centuries, whose members served as personal bodyguards to the Byzantine Emperors.
They are known for being primarily composed of Germanic peoples, specifically Scandinavians (the Guard was formed approximately 200 years into the Viking age) and Anglo-Saxons (after the Norman Conquest of England created an Anglo-Saxon emigration, part of which found employment in Byzantium).
Perhaps the most famous member of the Varangian Guard was the future King Harald Sigurdsson III of Norway, known as Harald Hardråde (“Hard-ruler”), who died at the Battle of Stamford Bridge while invading England in 1066.