Earth sheltered is one of the oldest forms of building. It is thought that from about 15,000 BC migratory hunters in Europe were using turf and earth to insulate simple round huts that were also sunk into the ground. The use of some form of earth sheltered construction is found across many cultures in history, distributed widely across the world. Normally these examples of cultures using earth sheltered buildings occur without any knowledge of the construction method elsewhere. These structures have many different forms and are referred to by many different names. General terms include pit-house and dugout.