'Walled Dyke' is actually a poor interpretation of the name. It actually means "Ridge-Ditch"
wale - O.E. wale "ridge," as of earth or stone, later "ridge made on flesh by a lash" (related to weal (2)); from P.Gmc. *walo. Used in reference to the ridges of textile fabric from 1583.
wale doesn't have any manmade implications, so 'walled' is not correct.
Dich is the Middle English for ditch, which is a very, very global word and comes from the Old English 'dc' which has roots in the Indo-European 'Dhg'. Dig and dyke obviously come from there too.
So, with Wale-dich you actually have a half Middle English, half Old English name.