Sesame-coated bread rings, a popular street food in Greece and Turkey (where they are called simit). Baked every morning–they're best when fresh–they are a traditional breakfast for workers.
Koulouri are believed to be a direct descendant of the ancient kollyra, a round bread served to slaves. In Byzantine times, they were sold in the streets of Constantinople and brought to Thessaloniki by refugees after the Fourth Crusade, at least according to one story. You can sometimes find them with poppy or flax seeds, or even fancy ones with fillings.
Image by Focalpoint, GNU Free Documentation License