A very strongly fortified citadel was built at Athelney by order of Alfred 8.
Primary Source Info
... arx munitissima ... regis imperio ... consita est.
Persons associated with this Event:
(the Great, king of the Anglo-Saxons, 871-899) : By order of the king (Alfred 8) a very strongly fortified citadel of very handsome construction was placed at the western end of the causeway.