The Roman baths were built in the 1st century BC following the Italian models from the 2nd to 1st centuries BC. They were a necessary public service in a Roman city. They served two purposes: first, they were thermal baths and a gym, while secondly they were also place where citizens could meet and interact. The Museum conserves the main quarters of the original building.
The palestra was a rectangular outdoor courtyard with an area with porches used for gymnastic exercise. Part of the palestra in the baths of Baetulo was later turned into a dressing room, which is still visible today.
The frigidarium was the room which held the cold-water baths, and it had a shallow pool where users could cool off after having practised exercises in the palestra. The tepidarium was a room with a temperate climate, a transition between the frigidarium and the caldarium, and it was used for hair removal, applications of ointment and massages.
The caldarium was the main room which housed the hot-water baths. It was covered with a vault, which helped to keep in the heat. A rectangular pool which was heated by a furnace or praefurnium is still conserved. The original mosaics that decorate the floor are particularly impressive.