For centuries, historians have searched for evidence that Tintagel Castle was the birthplace of King Arthur.

Perched on a rocky outcrop on the Cornish coast, the windswept site seemed an unlikely location for a royal court. But the discovery of a 1300-year-old windowsill has lent credence to the idea that Tintagel was, after all, the home of kings.

The two-foot long slate bears a mix of Latin and Greek with Christian symbols, in a decorative script similar to those found in illuminated Gospel manuscripts of the time, showing that the writer was familiar with those texts.

English Heritage, which manages Tintagel, said the find “lends further weight to the theory that Tintagel was a royal site with a literate Christian culture”.

The writing is believed to have been the work of someone practising their handwriting, perhaps carving words into the stone while gazing out to sea. It includes the Roman and Celtic names “Tito” and “Budic”, and the Latin words “fili”, or son, and “viri duo”, meaning “two men”. The Greek letter delta also appears.