Thermae be applied to those magnificent edifices which grew up under the empire, in place of the simple balneae of the republic, and which comprised within their range of buildings all the appurtenances belonging to the Greek gymnasia, as well as a regular establishment appropriated for bathing. Writers, however, use these terms without distinction. Thus the baths erected by Claudius Etruscus, the freedman of the Emperor Claudius, are styled by Statius "balnea", and by Martial "Etrusci thermulae". In an epigram by "Martial"—"subice balneum thermis"—the terms are not applied to the whole building, but to two different chambers in the same edifice.
Thermae adopted by Seneca to designate the bathroom of Scipio, in the villa at Liternum, and is expressly used to characterize the modesty of republican manners as compared with the luxury of his own times. But when the baths of private individuals became more sumptuous, and comprised many rooms, instead of the one small chamber described by Seneca, the plural "balnea" or "balinea" was adopted, which still, in correct language, had reference only to the baths of private persons. Thus Cicero terms the baths at the villa of his brother Quintus "balnearia". "Balneae" and "balineae", which according to Varro have no