Athens, Church of the Theotokos Parthenos/Atheniotissa

Also known as The Parthenon
Era 12AD
Location Athens 105 58, Greece

OK, so it's not a church anymore and there aren't any mosaics left on the walls. But it was once a church and it did have mosaics and given that it was dedicated to Mary, presumably a mosaic of her in some form. This may have been twelfth century. It may also have been the only mosaic in the church - Athens was not a very wealthy or important city at this point and we have no real way of dating mosaics or donor. But in 1848, the British Museum acquired 188 coloured and gold tesserae supposedly from Parthenon from Thomas Burdon, a long-time resident in Greece and there they still are. They haven't been displayed, as far as I know, and languish in a store (yes, I have seen them!)