1911 Encyclopædia Britannica/Frigidarium
FRIGIDARIUM, the Latin term (from frigidus, cold) applied to the open area of the Roman thermae, in which there was generally a cold swimming bath, and sometimes to the bath (see Baths). From the description given by Aelius Spartianus (A.D. 297) it would seem that portions of the frigidarium were covered over by a ceiling formed of interlaced bars of gilt bronze, and this statement has been to a certain extent substantiated by the discovery of many tons of T-shaped iron found in the excavations under the paving of the frigidarium of the thermae of Caracalla. Dr J. H. Middleton in The Remains of Ancient Rome (1892) points out that in the part of the enclosure walls are deep sinkings to receive the ends of the great girders. He suggests that the panels of the lattice-work ceiling were filled in with concrete made of light pumice stone.