Geothermal heating a total capacity of 15 GW extracted 88 PJ of heat energy for space heating. Global ground-source heat pump capacity is growing by 10% annually. Hot springs have been used for bathing at least since Paleolithic times. The oldest known spa is a stone pool on China's Mount Li built in the Qin dynasty in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. Geothermal energy supplied channeled district heating for baths and houses in Pompeii around 0 AD. In the first century AD, Romans conquered Aquae Sulis in England and used the
Aquae Flaviae of Trajan over the Tâmega River, whose existence marked a period of exceptional development of the city. Functioning as a crossroads, it controlled the routes to the mining districts. The remains of two epigraphic inscriptions are located on the bridge, commemorating the construction or remodelling by Emperor Trajan, as well as another that aroused various interpretations, the "Padrão dos Povos". The "Padrão dos Povos" mentions the civitates dependant of Aquae Flaviae: Aquiflavienses, Avobrigenses, Bibali, Coelerni, Equaesi, Interamici, Limici, Naebisoci, Querquerni and Tamagani, as well as the Roman Legio VII Gemina Felix legion. Aquae Flaviae was founded by Rome, although the