The Roman Baths complex is a site of historical interest in the English city of Bath. The house is a well-preserved Roman site for public bathing. The Roman Baths themselves are below the modern street level. There are four main features: the Sacred Spring, the Roman Temple, the Roman Bath House and the Museum holding finds from Roman Bath. The buildings above street level date from the 19th century. The Baths are a major tourist attraction and, together with the Grand Pump Room, receive more than one million visitors a year, with 1,037,518 people during 2009. It was featured on the 2005 TV program Seven Natural Wonders as one of the wonders of the West Country. Visitors can see the Baths and Museum but cannot enter the water. An audio guide is available in several languages. The water which bubbles up from the ground at Bath falls as rain on the nearby Mendip Hills. It percolates down through limestone aquifers to a depth of between 2,700 and 4,300 metres (8,900 and 14,100 ft) where geothermal energy raises the water temperature to between 64 and 96 °C (147.2 and 204.8 °F). Under pressure, the heated water rises to the surface along fissures and faults in the limestone. This process is similar to an artificial one known as Enhanced Geothermal System which also makes use of the high pressures and temperatures below the Earth's crust. Hot water at a temperature of 46 °C (114.8 °F) rises here at the rate of 1,170,000 litres (257,364 imp gal) every day, from a geological fault (the Pennyquick fault). In 1983 a new spa water bore-hole was sunk, providing a clean and safe supply of spa water for drinking in the Pump Room. The first shrine at the site of the hot springs was built by Celts, and was dedicated to the goddess Sulis, whom the Romans identified with Minerva. Geoffrey of Monmouth in his largely fictional Historia Regum Britanniae describes how in 836 BC the spring was discovered by the British king Bladud who built the first baths. Early in the 18th century Geoffrey's obscure 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,[10] engineers drove oak piles to provide a stable foundation into the mud and surrounded the spring with an irregular stone chamber lined with lead. In the 2nd century it was enclosed within a wooden barrel-vaulted building, and included the caldarium (hot bath), tepidarium (warm bath), and frigidarium (cold bath). After the Roman withdrawal from Britain in the first decade of the 5th century, these fell into disrepair and were eventually lost due to silting up, and flooding. The Anglo-Saxon Chronicle suggests the original Roman baths were destroyed in the 6th century. About 130 curse tablets have been found. Many of the curses related to thefts of clothes whilst the victim was bathing. he baths have been modified on several occasions, including the 12th century when John of Tours built a curative bath over the King's Spring reservoir and the 16th century when the city corporation built a new bath (Queen's Bath) to the south of the Spring. The spring is now housed in 18th-century buildings, designed by architects John Wood, the Elder and John Wood, the Younger, father and son. Visitors drank the waters in the Grand Pump Room, a neo-classical salon which remains in use, both for taking the waters and for social functions. Victorian expansion of the baths complex followed the neo-classical tradition established by the Woods. In 1810 the Hot Springs failed and William Smith opened up the Hot Bath Spring to the bottom, where he found that the spring had not failed but had flowed into a new channel. Smith restored the water to its original course and the Baths filled in less time than formerly. The visitor entrance is via an 1897 concert hall by J M Brydon. It is an eastward continuation of the Grand Pump Room with a glass-domed centre and single-storey radiused corner. The Grand Pump Room was begun in 1789 by Thomas Baldwin. He resigned in 1791 and John Palmer continued the scheme until its completion in 1799. The elevation on to Abbey Church Yard has a centre piece of four engaged Corinthian columns with entablatures and pediment. It has been designated by English Heritage as a grade I listed building.[19] The north colonnade was also designed by Thomas Baldwin. The south colonnade is similar but had an upper floor added in the late 19th century. The museum and Queen's Bath including the "Bridge" spanning York Street to the City Laundry were by Charles Edward Davis in 1889. It comprises a southward extension to the Grand Pump Room, in which some remains of the C17 Queen's Bath are merged. Bath was charged with responsibility for the hot springs in a Royal Charter of 1591 granted by Elizabeth I. This duty has now passed to Bath and North East Somerset Council, who carry out monitoring of pressure, temperature and flow rates. The thermal waters contain sodium, calcium, chloride and sulphate ions in high concentrations.