Delphi is an archaeological site and a modern town situated on the south-western slope of Mount Parnassus in the valley of Phocis. The Delphic oracle was the most important oracle in classical Greece. It was also a major site for the worship of the god Apollo. His sacred precinct in Delphi was a Panhellenic sanctuary, where every four years athletes from all over the Greek world competed in the Pythian Games. Delphi was renowned throughout the Greek world as the site of the Omphalos Stone which was thought to be the center of the Earth and the universe in antiquity.