What was the primary function of a hypocaust in Roman bathhouses?

The primary function of a hypocaust in Roman bathhouses was to heat the floors. This system was an innovative method of underfloor heating that utilized hot air generated by a furnace. The hot air would flow through spaces (or channels) beneath the raised floor, warming the surface above and creating a comfortable environment. The design allowed the heat to radiate evenly, making the bathing experience more pleasant and effective.

The other options do not accurately reflect the function of a hypocaust. Storing water pertains to facilities like water tanks or cisterns, changing clothes would typically involve areas designed for dressing and undressing, and providing light usually involves windows or lamps rather than heating systems. Therefore, the correct answer highlights the unique engineering of Roman bathhouses that contributed to their luxurious bathing culture.