'Hereward ... an Anglo-Saxon land-owner from the fens, who led local resistance ...'
Not surprisingly there was a lot of local resistance in those opening years, and of course some of the resistance stories later became legends - legends such as the story of Hereward the Wake and the siege of Ely. Hereward has been immortalised in ballads and stories and Victorian novels, all of them based on a real person - an Anglo-Saxon land-owner from the fens, who led local resistance against the Norman oppressors.
His allies in that resistance were real people too - we can identify them and their native villages. And we can go to what was the edge of the Cambridge fens, around the villages of Willingham and Over, north of Cambridge, and still see traces of Duke William's siege causeways, which were driven through the fen to overwhelm the Anglo-Saxons on the old 'isle of eels', Ely. The duke was not a man to cross.