Glastonbury Glastonbury, a town in Mendip District, Somerset, in the southwestern of England. It is famous as a historical religious center and for the many legends associated with it. A Celtic monastery existed on the site as early as the 4th century. By the 10th century the abbey here was one of the most important in England. The town declined after the dissolution of the monasteries in the 1530s. Legends assert that the first English Christian church was founded here in the 1st century CE by Joseph of Arimathea. Glastonbury is also identified with the Island of Avalon, of Arthurian legend. Nearby are the remains of an Iron Age lake village, which flourished from the 1st century BCE to the 1st century CE; it was built over a swamp on timber piles.