When the star-headed Old Ones on this planet had synthesized their simple food forms and bred a good supply of Shoggoths, they allowed other cell groups to develop into other forms of animal and vegetable life for sundry purposes, extirpating any whose presence became troublesome. With the aid of the Shoggoths, whose expansions could be made to lift prodigious weights, the small, low cities under the sea grew to vast and imposing labyrinths of stone not unlike those which later rose on land.
Source: wiktionary