Merlin's Oak, also known as the Old Oak and Priory Oak, was a pedunculate oak that once stood on the corner of Oak Lane and Priory Street in Carmarthen, South Wales. Merlin's Oak is associated with the legend of Merlin in the local lore, but it is also said to have been planted by a schoolmaster in 1659 or 1660, to celebrate the return of King Charles II of England to the throne. Legend had it that should the oak fall, disaster would befall the town.