The Roman Baths sprang up around the settlement of Aquae Sulis, which had been a Celtic religious center for centuries before the Romans arrived. The town was built around a sacred hot spring, which was dedicated to the localized Celtic goddess Sulis.
When the Romans took control of the area, they enacted their standard religious policy of merging local deities with Roman ones. Sulis became Sulis-Minerva, bonded with the Roman goddess of wisdom, and a temple was founded. Visitors would toss offerings into the spring and beseech Sulis-Minerva for aid.
The complex grew into a prominent bathhouse and survived up until the Romans left Britain in 410 AD before being falling into disrepair. At its largest extent in the 3rd Century AD, the bathhouse included a hot bath (caldarium), a tepid bath (tepidarium), and a cold bath (frigidarium) along with several other facilities.