Here there is one of the engineering secrets of the ancient Romans, who did so much to improve their quality of life, a secret intimately connected to those extraordinary public baths that were a source of pride for the entire ancient Roman civilization. What you see in the picture is a praefurnium, the way in which the Romans heated the water in their baths.

Places of pleasure, hygiene and social gathering, the Roman baths were mainly composed of three rooms: the frigidarium (a large room with a series of pools in cold water), the tepidarium (lounge with lukewarm water) and the calidarium. The whole represents a real session of psycho-physical well-being, an architectural complex that also housed bookcases and gyms, halls entirely decorated with marble slabs and mosaics, a place where, therefore, it was possible to restore both the body and the mind, in different ways and manners. Above all the calidarium was the top for a self-respecting Roman, as a bit like in modern saunas everything was focused on relaxation, often accompanied by the company of friends or others welcome guests. Imagine a room with tubs leaning against the wall, with steps inside on which the Romans could sit, enjoying the hot water. And now, the question is: how did they heat the water?

Here we have the praefurnium. Below the floor of the calidarium (particularly under the water-filled tubs) there were a series of small ovens. Underground places where slaves took care to always keep a flame alive, whose hot vapors were channeled into the tubuli, which were terracotta pipes that ran along the perimeter of the entire pool and room. Small rooms, narrow tunnels, long pipes, small ovens, a real complex and inextricable underground world that gave the Romans that psycho-physical pleasure sought in the spa! Finally imagine what hell those slaves could experience who, day after day, walked inside the underground tunnels sometimes invaded by smoke, always very hot and with an unbreathable air. Unfortunately for them the slaves, according to Roman legislation, were not even human beings and, consequently, very few thought about their well-being. People who tirelessly worked to give that relaxation and physical well-being sought by people from different social backgrounds, not just aristocrats. This preafurnium, photographed in one of the spas of the archaeological park of Ostia Antica, is therefore a direct historical witness of the complex organizational and engineering machine that was behind large buildings such as the spas but which, at the same time, worked thanks to the tireless work of slaves.