I ran across a picture of the above sculpture yesterday in Peter Brown's so-far excellent The World of Late Antiquity and was stunned.
When do you think the sculpture was made? 800 AD? 1000 AD?
In fact the sculpture is of the Emperor Diocletian and the three other members of the Tetrarchy - circa 300 AD.
Prof. Brown notes that "This simplified, military group was so medieval in tone that the individuals were long mistaken for Christian crusaders, and even worshipped as statues of Saint George!"
This is what a Roman bust of Diocletian should look like - except that it was created in the 17th Century:
I could go on about how this symbolizes perfectly the impossibility of identifying a specific date on which late Roman civilization transformed into the medieval world, but I'll spare you.