In what century was this castle erected that was destroyed and replaced several times and whose name is derived from the common Scottish surname Douglas?
Douglas (surname): Douglas (occasionally spelled "Douglass") is a common surname of Scottish origin, thought to derive from the Gaelic "dubh glas", meaning "black stream". Douglas (surname):  While there are numerous places with this name in Scotland, it is thought, in most cases, to refer to Douglas, South Lanarkshire, the location of Douglas Castle, the chief stronghold of the Lords of Douglas.
i don't know