From Novinite:

A unique Roman ritual plate from the middle of the 3rd century A.D. has been discovered during excavations in Bulgaria's spa resort of Hissar, the Bulgarian National Television reported Thursday.

The plate was discovered in one of the rooms of the Roman thermal baths, and provides new information about the late antiquity complex in the ancient Roman town of Diocletianopolis, at whose place today's Hissar is located.

The marble plate with size of 50 cm x 50 cm shows the three nymphs, who were believed to be guardians of the mineral springs in the town. The heads of the women's illustrations are damaged by the water but as a whole the plate is very well preserved.

"The work of the ancient master was really precise. The folds of the nymph's are really well-defined", said Mitko Madzharov, the Director of the Hissar Archeological Museum.

The plate has inscriptions in Greek, from which it is understood that it was made by a Roman aristocrat as a sign of gratitude for his curing. It also provides new information about the time of origin of the thermal baths complex. It was believed to have been built in the fourth century but now the archeologists relate it to the third century A.D. The place is now thought to have been a nymphs' altar.

The town of Hissar in central southern Bulgaria has an ancient history of about six thousand years. The Thracian village there was later turned into a town by Romans and named Diocletianopolis after Emperor Diocletian (285-304) stopped there because of the mineral baths.

The original article is accompanied by a photo:

... which seems to suggest that 'plaque' was the word they were looking for ...