Sulis to various Indo-European words for "sun" (cf. Homeric Greek ηέλιος, Sanskrit "sūryah" "sun", from Proto-Indo-European "*suhlio-"). Sulis was the local goddess of the thermal springs that still feed the spa baths at Bath, which the Romans called "Aquae Sulis" ("the waters of Sulis"). Her name primarily appears on inscriptions discovered at Bath, with only a single instance outside of Britain at Alzey, Germany. This is not surprising, as Celtic deities often preserved their archaic localisation. They remained to the end associated with a specific place, often a cleft in the earth, a spring, pool or well. The Greeks referred to
Geothermal energy a renewable energy source like geothermal. But as a result of government assisted research and industry experience, the cost of generating geothermal power has decreased by 25% over the past two decades. In 2001, geothermal energy costs between two and ten US cents per kWh. Hot springs have been used for bathing at least since Paleolithic times. The oldest known spa is a stone pool on China's Lisan mountain built in the Qin Dynasty in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. In the first century AD, Romans conquered "Aquae Sulis",