Not far from the Forum, we can see the most important thermal complex of Ostia. The Forum's thermal baths were built starting from 150 A.D., under Antonino Pio, and transformed several times until the fifth century. The system was designed according to the optimal exposure considering the afternoon use: as a matter of fact, the various rooms were facing south and arranged in a set of steps in order to make the most of the light and heat of the sun.
The main building, dating back to the first construction, included the frigidarium (cold water swimming pool), an elliptical sudatorium (sweating room), the tepidarium (warm water swimming pool) and the calidarium (hot water swimming pool). The rooms were characterized by their original and varied shape, associated with their different functions. A narrow corridor led to an open space, colonnade, which served as a gym.
The entire complex was warmed up in the basement. There was also a cistern from which, thanks to a wheel with a diameter of about ten meters the water rose to the surface.