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View looking southeast at the well-preserved and partially reconstructed Hot Room (caldarium). Note the small columns that supported the floor—a portion of the floor (upper right) is a modern reconstruction.
Left of center note the two very bright areas. Outside of these was the furnace (hypocaust) and the heated air entered the caldarium from there, circulated under and heated the floor before passing up clay pipes embedded in the walls—modern reconstruction of these pipes are visible in the upper most portion of the image.
Thus the floor and the walls of this structure were heated.