The fundamental part of the Roman Baths is the sacred spring. Hot water at a temperature of 460°C rises here at the rate of 1,170,000 liters (240,000 gallons) every day and has been doing so for thousands of years. To the ancients, this remarkable phenomenon could only be the work of the gods.

The first shrine at the springs in Bath was built by the Celts, and dedicated to the goddess Sulis. After the Roman invasion, Sulis was identified with the Roman goddess Minerva, but the name Sulis continued to be used. This led to the town's ancient Roman name of Aquae Sulis ("waters of Sulis").

During the Roman occupation of Britain, increasingly grand temples and bathing complexes were built. The bath complex in Bath was founded in 75 AD. The healing powers of the goddess and the mineral-rich water from the spring attracted visitors from across the Roman Empire.