It was the last of the four halls next to the caldarium. Under Constantine the Great the "caldarium" was modified. The "caldarium" faced southwest, the "frigidarium" northeast. Two octagonal halls flanked the "caldarium". Next to the "caldarium" were saunas ("laconica"). The water would be heated by fire then channelled into the caldarium (hot bathing room). It was followed by the frigidarium, the tepidarium and caldarium. The caldarium and some other features of the baths are visible. The rooms of these springs consisted of a raised pool in the caldarium, latrines etc. This led to various types of heated rooms including caldarium, tepidarium, laconicum/sudatorium, and the frigidarium. The Roman bathhouse consisted of three areas, the caldarium, the tepidarium, and the frigidarium. The caldarium was covered with marble slabs. In 1878/9, Giuseppe Fiorelli discovered mosaics in the caldarium and western "palaestra". Dressing rooms, also known as apodyteria, were located on either side of the caldarium. Temperatures in the caldarium could reach 40 degrees Celsius (104 degrees Fahrenheit).