|Viking graffiti: Near the ramp one takes to go upstairs in the Aya Sofya is a sign showing pictures of all the things to be seen up there. One of the pictures showed some rune-like scratches and said, "Viking graffiti". No further explanation. (In general, museum signs in Istanbul didn't give much information; our friend, Rudy, says that it's that way on purpose to ensure business for the tour guides.) Sure enough, there is something that looks like Viking graffiti scratched into a stone handrail above the altar.
All I have figured out from searching around the Internet is that the Ottoman Sultans hired Vikings as guards. The Vikings would come down to Istanbul by way of Russia.
Here Frances looks irritated because I kept making her pose for "just one more picture" of the graffiti.