Tintagel (tĭntāˈjəl) [key], small town, Cornwall, SW England. It is S of Tintagel Head, a promontory connected to the mainland by a narrow, rocky neck of land. The ruined Tintagel Castle, which extends from the promontory across the isthmus, was built in the 12th cent. on the site of a Celtic monastery. The area is the reputed birthplace of King Arthur. Within the town's vicinity are several old structures, including a 14th-century stone hut that serves as a post office.