I found this really cool story on Futility Closet's blog here.
"In 1857 archaeologists unsealed an ancient house on the Palatine Hill in Rome. Inside, carved into the plaster of one of the walls, they found this inscription.
"It appears to show a donkey-headed figure attached to a cross. A young man raises his hand to it, perhaps in worship. Below this is written in crude Greek, 'Alexamenos worships [his] God.'
"It’s believed to be one of the first representations of the crucifixion of Jesus."