John Leland, the 16th century expert on Arthurian legend, identified the bridge between Street and Glastonbury as the place where King Arthur’s sword Excalibur was cast into a lake. Archaeological work has confirmed that in the early medieval period a bridge and lake really did actually exist in that very location.
The bridge over the River Brue, and its associated stone causeway, were created sometime between c. AD 650-780, at a time when Glastonbury Abbey acquired large landholdings on the Polden Hills near Street. It lasted until its replacement by a new bridge in the 12th century, which itself was replaced in the 19th century.
The early bridge and causeway had been built on the upstream side of a shallow lake. The memory of these ancient features no doubt inspired the link to the legend of Excalibur and the site ‘wher men fable that Arture cast in his Swerd‘ as John Leland recorded.
REF: Brunning, R. 2010. Taming the floodplain: River canalisation and causeway formation in the Middle Anglo-saxon period at Glastonbury, Somerset. Medieval Archaeology, 54, 319-328