 Much more is known of the hundreds of unique cleitean that decorate the archipelago . These dome @-@ shaped structures are constructed of flat boulders with a cap of turf on the top . This enables the wind to pass through the cavities in the wall but keeps the rain out . They were used for storing peat , nets , grain , preserved flesh and eggs , manure , and hay , and as a shelter for lambs in winter . The date of origin of this St Kildan invention is unknown , but they were in continuous use from prehistoric times until the 1930 evacuation . More than 1 @,@ 200 ruined or intact cleitean remain on Hirta and a further 170 on the neighbouring islands . House no . 16 in the modern village has an early Christian stone cross built into the front wall , which may date from the 7th century . 
