A passage from Bede’s ‘Thirty Questions on the Book of Kings’ states:

In accordance with the custom of cities, Samaria must have had earth (piled) next to its interior walls and nearly level with them so that the walls would not, for want of a supporting embankment, be destroyed by the repeated blows of a ram.

This suggests to me that Anglo-Saxon fortifications possibly had interior earth banks as Bede certainly never left the country and presumably based his knowledge of defensive fortifications on contemporary practices. But I don’t know of any archaeological findings that confirm or disprove the idea.