Archaeologists digging in the ruins of Nevern Castle in Wales have found a dozen pieces of slate with scratched markings of stars and other designs.
The slates were found at a 12th century doorway, hinting that they were put there to ward off evil spirits trying to get into the entrance. I wrote about this practice on a previous Medieval Mondays, in which hidden clothing is used to ward off witches. Dead cats work too!
The archaeologists say they were installed around 1170-1190 when the castle was rebuilt in stone. The castle was originally built by the Normans as a motte-and-bailey castle in 1108. The BBC has a nice photo of one of the Nevern slates. Recent excavations have unearthed a lot of interesting finds from this site, including a game of Nine Men's Morris shown below. Thanks to Wikimedia Commons for this photo.