Creation is believed to be the work of culture heroes who travelled across a formless land, creating sacred sites and significant places of interest in their travels. In this way, "songlines" (or "Yiri" in the Warlpiri language) were established, some of which could travel right across Australia, through as many as six to ten different language groupings. The dreaming and travelling trails of these heroic spirit beings are the songlines. The signs of the spirit beings may be of spiritual essence, physical remains such as petrosomatoglyphs of body impressions or footprints, among natural and elemental simulacra.