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
Roman Baths (Bath) legend was given great prominence as a royal endorsement of the waters' qualities, with the embellishment that the spring had cured Bladud and his herd of pigs of leprosy through wallowing in the warm mud. The name Sulis continued to be used after the Roman invasion, leading to the town's Roman name of "Aquae Sulis" ("the waters of Sulis"). The temple was constructed in 60–70 AD and the bathing complex was gradually built up over the next 300 years. During the Roman occupation of Britain, and possibly on the instructions of Emperor Claudius, engineers drove oak piles to provide a