Roman baths. Cutaway artwork of the typical layout of a grand Roman public bathhouse, with arrows (green) showing the route from the entrance to the exit through the complex of baths (thermae). These are the Baths of Diocletian (Thermae Diocletiani) in Rome, the largest of the grand imperial baths, built between 298 and 306 AD. The bathing route passed through the natatio (swimming pool) along the centre of the building through the frigidarium (cold room), the domed tepidarium (warm room), and the caldarium (hot room). Another bath is at upper right. The final rooms were the palaestra (exercise yard) and dressing areas (apodyterium or vestibule).