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 Castle:  The first castle, erected in the 13th century, was destroyed and replaced several times until the 18th century when a large mansion house was built in its place.
i don't know