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 Iasae part of the Roman settlement was located on the highest terrace of the hill Varaždin spa, today the park and archaeological site. The residential part of "Aquae Iasae" was on the terraces that descend to the foot of the hill in the foothills of the craft-established commercial and trade show facilities. At the end of 3rd century AD Aquae Iasae were ravaged during the incursion of the Goths, then in the beginning of the 4th century the "thermae" were restored by Emperor Constantine. The resort was completely ruined and deserted in the 4th century during the invasions of the Migration