"Remains of substantial walls pre-dating the 16th Century barn at Dunster were unearthed during work to convert the building into a community centre.
Experts said the two walls, paving and glazed tile fragments were almost certainly part of the Benedictine Priory of Dunster dating back to 1127.
The finds have been recorded and grassed over for safe-keeping.
Bob Croft, Somerset County Council's County archaeologist, said the finds suggest a wealth of history below the surface.
"This shows there is considerable potential for the survival of more medieval remains associated with the Priory," he said."