The Sacred Spring lies
at the very heart of the ancient monument. Water rises here at the
rate of over a million litres a day and at a temperature of
460C. The Spring rises within the courtyard of the
Temple of Sulis Minerva and water from it feeds the Roman baths.
There is some slight evidence, an earthen bank projecting into the
Spring, that suggests it was already a focal point for worship
before the Roman Temple and baths were built.
Roman engineers surrounded the Spring with an irregular
stone chamber lined with lead. To provide a stable foundation for
this they drove oak piles into the mud. At first this reservoir
formed an open pool in a corner of the Temple courtyard but in
the second century AD it was enclosed within a barrel vaulted
building and columns and statue bases were placed in the Spring
itself. Enclosing the Spring in a dimly lit building in this way
and erecting statues and columns within it must have enhanced the
aura of mystery that surrounded it. Offerings were thrown into the
Spring throughout the Roman period.
Eventually the vaulted building collapsed into the Spring
itself. We do not know when this was, but it is likely to have been
in the sixth or seventh century. The oak piles sunk into the mud
two thousand years ago continue to provide a stable foundation for
the Roman reservoir walls today.