According to 24-Hour Museum:
The [Pictish stones of St. Vigeans], which date back to the decades before the nation of Scotland was born in the 9th century, depict ornate Christian crosses and fantastic beasts and bear both Latin and Pictish writing (the latter now indecipherable). . . .
The stones are a great early Christian treasure of Angus. They include the Drosten Stone, a cross slab with ornate cross and fantastic beasts, plus a rare Latin and Pictish inscription which might have commemorated King Uoret who died around 842AD. In 843AD, the Pictish kingdom was united with Gaelic Dalriada under a single monarch – leading to the birth of Scotland.
Read more about the Picts here.