The Norman invasion of 1066 brought with it a change of ruler and a change of fortune for the town. In 1088 Bath was involved in a revolt against the rule of King William II. Using Bristol as a base, rebel Norman bishops ravaged Bath and the surrounding area. The town and countryside were plundered and little remained of the once thriving community.
In the same year, the King appointed John of Tours (de Villula) Bishop of Wells. A few years later, for £500 in silver, John bought the town of Bath from the King and moved his See (seat of power) from Wells to Bath. This reduced Wells to the level of a simple collegiate church, causing rifts between the monks of Bath and the canons of Wells that were to last until the 13th Century. John set about building a cathedral on the site of the former monastery. This was to be three times the size of the present day Abbey and occupied a quarter of the town. The timber construction led to a number of serious fires, most notably in July 1137 when the blaze devastated the city and cathedral.
The town now became a city by prescription. In 1157, Bishop Robert persuaded the Pope to acknowledge formally that Bath was the seat of the Bishopric. This was later confirmed by the Charter of 1256 from Henry II who referred to the "City of Bath". The Charter of Incorporation granted by Elizabeth I in 1590 made Bath a city in its own right.
In 1180, Bishop Reginald Fitzjocelyn founded the Hospital of St John the Baptist to care for the poor and sick who used the baths. Other baths were built around the city to cater for the ever-increasing population of lepers who were attracted to Bath seeking a cure from the waters. During this time there were three baths in use: King's, Cross and Hot. It is possible that the King's Bath was renovated during the reign of Bishop John of Tours, due to his background as a physician.