The excavation revealed the particularly interesting hypocaust structure of the apse. An opus vittatum wall, found abutting the exterior of the apse in the north-western corner of the excavation, formed one side of the furnace room which provided the hot air directly to below the pavement in the apse. The apse walls, faced with bricks, terminated up against the long blocks of peperino which supported the base of the arch. These blocks were positioned at a right angle to the aperture and were decorated with simple triglyph and metope motifs. On the northern side of the aperture, a sculpted base with a moulding was positioned against the stone blocks so as to form a long line which extended into the apse to two thirds of its depth. These blocks, too highly decorated for their function and position, must have been re-used from a preceding building or have belonged to an earlier phase of the baths. The sculptured blocks, if replaced in their original positions, parallel to those still in situ, form a conduit which could have been used as a chimney for the furnace. The apse floor was paved with large terracotta tiles. The remaining part of the apse was constituted by a regular series of pilae resting on a clay pavement.

The channel or air conduit is an archaic characteristic, which in the typological development of Roman baths precedes the hypocaust resting on pilae. This may be evidence of the type and the existence of an earlier phase of the baths, perhaps dating to the city’s foundation. Of note, amongst the material found, was a mosaic in the rectangular room, with white, black and red tesserae, with no clear pattern. Where the bathers would have passed from the rectangular room into the apse, in line with the air conduit and furnace opening, several tesserae where set in a longitudinal position so as to create a sort of “flowing” motif. The pattern could lead towards a door or stair in the apse or indicate that the pavement was hotter. Several fragments of thin glass were found (some decorated with silver leaf), together with fragments of architectural nails, two fragments of polished bone, yellowish amber (jewellery?), a coin possibly of Valentinian I or Valens and datable to 370-380 A.D. and numerous fragments of black glaze pottery dating to the 3rd century B.C. the period of the city’s foundation.

Before the excavation, from the structures visible on the surface and the plan published by Ciotti, the form of the baths looked like that of the so-called “bath with the Greek hypocaust” at Olympia, which is often cited in discussions sustaining that the hypocaust was of Greek origin. Recent studies now date its invention to between 100-40 B.C. This would place the origins of the hypocaust technique in Italy to probably the mid second century B.C. The similarities between the above ground structures of the two baths are surprising: an open apse at the centre leads into a rectangular room with two room off to one side. The proportions and positioning are also similar: both are small with respect to baths of imperial date and are positioned in marginal areas as though intended more for use by visitors (for purification) than for daily ablutions by the inhabitants.

The excavation of the apse revealed enormous differences below ground. The aperture of the apse at Carsulae and the furnace entrance, with conduit functioning as a chimney outside of it. At Olympia the apse is broken up by the basin and the furnace positioned on the opposite side of, and behind the rectangular room. The entire pavement is covered by pilae.

The similarities may suggest a closeness in date, with the hypocaust model at Carsulae seeming to be the earlier. However, the construction materials and methods at Carsulae move the date back to the mid 2nd century B.C. and suggest numerous phases of construction and restructuring. Moreover, the re-use of decorated blocks from earlier buildings, the presence of opus reticulatum and incertum in the baths structure proves that the architects at Carsulae had reconstructed the original form and preserved the archaic character of the baths for centuries. (MiBAC)