A view of the Roman Baths, with the Bath Cathedral in the background. The natural hot springs that feed these baths were here before the Romans. Celtics / native Britons used the hot spring for bathing, but without the elaborate structure. The springs were surrounded by marshes, so it was not frequently used. The area around the springs was, at that time, marshy, until the Romans built it up into these elaborate structures. Obviously, to both cultures, the idea of a warm spring was incredible, so they thought the sight was divine. Now we know how the water is naturally heated, but they thought it was the work of gods / goddesses.