Architecture and technology
Baths could be called either thermae ("warm baths") or balnea. Building catalogues of Rome from the fourth century, the Notitia regionum urbis Romae and the Curiosum urbis Romae regionum XIV, list 11 thermae and 856 balnea (but the total number of balnea given is greater than the added numbers per region: 967 and 942). The way in which Martialis uses the words suggests, that the former denomination was used when baths were lavishly decorated, being large or small, privately owned or work of the Emperor. The latter denomination was used for the average, more common establishments.
Some baths were named after the Emperor, either because he was the builder, or as a sign of devotion (for example Balineum Hadrianum and Thermae Severianae). Others were named after private financiers (for example Thermae Cassiorum and Balneum Terenti Donati). Still others received their name from deities or special features (for example Thermae Herculis, Thermae Silvani, Balneum Veneris and Balneum Novum).
The architect Vitruvius wrote down instructions for the construction of baths, in the first century BC:
Primum eligendus locus est quam calidissimus, id est aversus ab septentrione et aquilone. Ipsa autem caldaria tepidariaque lumen habeant ab occidente hiberno, sin autem natura loci inpedierit, utique a meridie, quod maxime tempus lavandi a meridiano ad vesperum est constitutum. Et item est animadvertendum uti caldaria muliebria et virilia coniuncta et in isdem regionibus sint conlocata. Sic enim efficietur ut in vasaria et hypocausis communis sit eorum utrisque. Aenea supra hypocausim tria sunt componenda, unum caldarium, alterum tepidarium, tertium frigidarium, et ita conlocanda uti ex tepidario in caldarium quantum aquae calidae exierit, influat de frigidario in tepidarium ad eundem modum, testudinesque alveolorum ex communi hypocausi calefaciantur.
Suspensurae caldariorum ita sunt faciendae ut primum sesquipedalibus tegulis solum sternatur inclinatum ad hypocausim, uti pila cum mittatur non possit intro resistere sed rursus redeat ad praefurnium ipsa per se. Ita flamma facilius pervagabitur sub suspensione. Supraque laterculis bessalibus pilae struantur ita dispositae uti bipedales tegulae possint supra esse conlocatae. Altitudinem autem pilae habeant pedes duo eaeque struantur argilla cum capillo subacta, supraque conlocentur tegulae bipedales quae sustineant pavimentum.
Magnitudines autem balinearum videntur fieri pro copia hominum, <dummodo> sint ita dispositae. Quanta longitudo fuerit, tertia dempta, latitudo sit praeter scholam labri et alvei. Labrum utique sub lumine faciundum videtur, ne stantes circum suis umbris obscurent lucem. Scholas autem labrorum ita fieri oportet spatiosas uti cum priores occupaverint loca, circum spectantes reliqui recte stare possint. Alvei autem latitudo inter parietem et pluteum ne minus sit pedes senos, ut gradus inferior inde auferat et pulvinus duos pedes.
Laconicum sudationesque sunt coniungendae tepidario, eaeque quam latae fuerint, tantam altitudinem habeant ad imam curvaturam hemisphaerii. Mediumque lumen in hemisphaerio relinquatur ex eoque clupeum aeneum catenis pendeat, per cuius reductiones et demissiones perficietur sudationis temperatura. Ipsumque ad circinum fieri oportere videtur, ut aequaliter a medio flammae vaporisque vis per curvaturae rotundationes pervagetur.In the first place, the warmest possible situation must be selected; that is, one which faces away from the north and northeast. The rooms for the hot and tepid baths should be lighted from the southwest, or, if the nature of the situation prevents this, at all events from the south, because the set time for bathing is principally from midday to evening. We must also see to it that the hot bath rooms in the women's and men's departments adjoin each other, and are situated in the same quarter; for thus it will be possible that the same furnace should serve both of them and their fittings. Three bronze cauldrons are to be set over the furnace, one for hot, another for tepid, and the third for cold water, placed in such positions that the amount of water which flows out of the hot water cauldron may be replaced from that for tepid water, and in the same way the cauldron for tepid water may be supplied from that for cold. The arrangement must allow the semi-cylinders for the bath basins to be heated from the same furnace.
The hanging floors of the hot bath rooms are to be constructed as follows. First the surface of the ground should be laid with tiles a foot and a half square, sloping towards the furnace in such a way that, if a ball is thrown in, it cannot stop inside but must return of itself to the furnace room; thus the heat of the fire will more readily spread under the hanging flooring. Upon them, pillars made of eight-inch bricks are built, and set at such a distance apart that two-foot tiles may be used to cover them. These pillars should be two feet in height, laid with clay mixed with hair, and covered on top with the two-foot tiles which support the floor.
The size of the baths must depend upon the number of the population. The rooms should be thus proportioned: let their breadth be one third of their length, excluding the niches for the washbowl and the bath basin. The washbowl ought without fail to be placed under a window, so that the shadows of those who stand round it may not obstruct the light. Niches for washbowls must be made so roomy that when the first comers have taken their places, the others who are waiting round may have proper standing room. The bath basin should be not less than six feet broad from the wall to the edge, the lower step and the "cushion" taking up two feet of this space.
The laconicum and other sweating baths must adjoin the tepid room, and their height to the bottom of the curved dome should be equal to their width. Let an aperture be left in the middle of the dome with a bronze disc hanging from it by chains. By raising and lowering it, the temperature of the sweating bath can be regulated. The chamber itself ought, as it seems, to be circular, so that the force of the fire and heat may spread evenly from the centre all round the circumference.Vitruvius, De Architectura V,10,1-2 and 4-5. Translation: Morris Hicky Morgan. The Roman baths are characterized by communal pools and a sequence of different bathing rooms (baths of the Greek type are characterized by individual tubs and a less clear lay-out). To some extent, types of baths can be distinguished: with rooms in a row, with rooms in a ring, with double rows, with double rooms, and so on. However, many variations have been found that do not conform to any type.
The bathers moved from warm to hot to cold rooms. The heating system, called hypocaustum, is well-known: hot air circulated below raised floors resting on tiny brick piers (suspensurae) and through terracotta pipes set against the walls (tubuli). The rooms and the water in the pools were heated in this way, the water sometimes also in a special, copper or bronze cauldron called testudo, "tortoise", after the shape. The ovens (praefurnia) were fired with wood, and located in a service area that was hidden from the view of the visitors. In these narrow, dark corridors many oil lamps have often been excavated.
The dressing room was called apodyterium. It often had rows of small niches in which clothes could be stored. Presumably the visitors put on special wooden shoes here, as protection against slipping and the heat of the floors. The body was rubbed in with oil. The heated rooms were oriented to the south, so that they received as much sunlight as possible. In the facade could be high and wide windows, containing large glass window panes. The hot and cold bath (caldarium and frigidarium) always had pools, the lukewarm bath (tepidarium) sometimes, but always a heated floor. We know that sweating rooms existed (laconica, sudatoria), but these are difficult to identify. The same is true for the heliocaminus, a room for sunbathing, and for the destrictarium, the place where the body was rubbed down with towels and bronze scrapers (strigiles). A large open area, the palaestra, was used for various games, especially ball games, and physical exercise, such as wrestling and weightlifting. In some baths, masseurs could be hired (unctores, "anointers").
Dressing room (apodyterium) of the Forum Baths in Pompeii. Photo: Wikimedia, Aleksandr Zykov.
