A similar arrangement (called testudo alvei by Vitruvius) probably existed for the alveus in the caldarium on the other side; but that part of the men's baths has been destroyed. Only one other heater of this kind has been found,—and that much smaller,—in a villa near Boscoreale, recently excavated; but the semicircular opening made for the heater above the hot air flue may be seen in the Central Baths, in a private establishment at Pompeii, and generally in the remains of Roman baths.

In the furnace room (praefurnium, IX) between the two caldariums, stood three large cylindrical tanks. They have disappeared, but their outlines can still be seen in the masonry of the foundations, and are shown in our plan. The one furthest east was for hot water. It was directly over the fire, and connected with the bath basins of the two caldariums. The next, for lukewarm water, stood over a hollow space opening into the furnace. A lead pipe leading from it to the labrum of the women's caldarium is still to be seen; the water bubbled up in the middle of the labrum. The third and largest reservoir, for cold water, was placed on a foundation of solid masonry.

The more important alterations made in the baths during the two centuries that they were in use had to do with the arrangements for heating, and may briefly be considered here before we proceed to another part of the building. It will be best not to weary the reader with details, but to present a brief summary of conclusions, which will perhaps be found of interest, not only as casting light on the gradual development of these baths, but also as illustrating that adjustment of public buildings to the needs and tastes of successive generations, which was as characteristic of ancient as it is of modern life.

For the extensive changes made in the earlier part of the first century B.C. we have the evidence of an inscription, which had been cast aside and was found in one of the smaller rooms. It reads, C. Uulius C. f., P. Aninius C. f., II v. i. d., Laconicum et destrictarium faciund. et porticus et palaestr[am] reficiunda locarunt ex d[ecurionum] d[ecreto] ex ea pequnia quod eos e lege in ludos aut in monumento consumere oportuit faciun[da] coerarunt eidemque probaru[nt]. The form of the letters and the spelling point to the time of Sulla as the period in which the inscription was cut. The syntax is confused, but the meaning is clear: a Laconicum and destrictarium were built, the colonnade and palæstra repaired, by the duumvirs Gaius Ulius and Publius Aninius, in accordance with a vote of the city council; and they furnished the means for this work in fulfilment of their obligation, incurred by the acceptance of the duumviral office, to spend a certain sum upon either games or buildings.

The destrictarium—a room for removing dirt and oil with the strigil after gymnastic exercises—is easily identified (D), as are also the palaestra and colonnade; but in our survey of the baths, we have found no separate chamber to which the term Laconicum could properly be applied. In order to arrive at a solution of the difficulty, we must note the successive steps by which, as shown by an examination of the remains of the masonry, the heating arrangements were extended and improved.

At first, in the Baths as originally constructed, there were neither hollow walls nor hollow floors. The heating was done by means of braziers; and there were niches or lockers in the walls of the caldariums and tepidariums similar to those now found in the dressing rooms, but in double rows, the upper niches being larger, the lower smaller.

Later, a hollow floor was built in the men's caldarium. Later still, this room was provided with hollow walls, which were extended to the crown of the ceilings and the lunettes, the tepidarium being still heated with braziers.

Finally, a hollow floor and hollow walls were constructed at the same time in the men's tepidarium, but the hot air chamber was not carried up into the ceiling or the lunettes.

A similar transformation was gradually accomplished in the women's apartments; but owing, it would seem, to a desire for greater warmth in the tepidarium, the hot air chamber here, as in the caldarium, was extended to the lunettes and the ceiling.