 Extensive ruins of field walls and cleitean and the remnants of a medieval ' house ' with a beehive @-@ shaped annexe remain . Nearby is the ' Bull 's House ' , a roofless rectangular structure in which the island 's bull was kept during winter . Tobar Childa itself is supplied by two springs that lie just outside the Head Wall that was constructed around the Village to prevent sheep and cattle gaining access to the cultivated areas within its boundary . There were 25 to 30 houses altogether . Most were blackhouses of typical Hebridean design , but some older buildings were made of corbelled stone and turfed rather than thatched . The turf was used to prevent ingress of wind and rain , and the older " beehive " buildings resembled green hillocks rather than dwellings . 
