Skara Brae's inhabitants were apparently makers and users of grooved ware, a distinctive style of pottery that appeared in northern Scotland not long before the establishment of the village. The houses used earth sheltering but, being sunk into the ground, they were built into mounds of pre-existing domestic waste known as middens. Although the midden provided the houses with a small degree of stability, its most important purpose was to act as a layer of insulation against Orkney's harsh winter climate. On average, the houses measure 40 square metres (430 sq ft) in size with a large square room containing a hearth which would have been used for heating and cooking. Given the number of homes, it seems likely that no more than fifty people lived in Skara Brae at any given time.
See also: http://www.pbase.com/light_works/image/151077399
Reference: http://en.wikipedia.org/wiki/Skara_Brae