No it wasn't aliens. It was ancient Zulu tribesmen from Africa who quarried the stone from the diamond mines and transported the monoliths to Albion on giant ancient African cargo planes.
Of course this was long before the blue-eyed devils stole all their technology and burned all the African libraries, leaving them for centuries without a pot to p*ss in.
Right but the real trick was wiping the memory and knowledge from the minds of these advanced thinkers.