Francis Blomefield,
History of Norfolk — Chapter 2
“ Alfred the Great had wholly subdued the Danes, the author of his life tells us, that finding the earth walls which encompassed the Saxon fortifications not strong enough to resist a furious enemy, he erected strong castles and forts of brick and stone, and among others, improved the fortifications of this castle, and (as I think) erected the first castle of brick and stone that ever was built here ”
