In the House of the Cistern four units can be recognized: the original Hadrianic building; a bakery in the north and central part; water-wheels and cisterns in the south part, related to nearby baths; a late antique exedra in the north part. The exedra, I,XII,3, is described separately.

The Hadrianic remains

In the north part of the building are a few remains of a very large octagonal room from the Hadrianic period. The room contained four large semicircular niches, starting at floor level. The north-east one was obliterated by Exedra I,XII,3, the north-west one is preserved badly. The south-west niche - with the exception of the west part, the reconstruction of which is hypothetical - and especially the south-east one - in which an oven was installed - are preserved quite well, with a maximum height of a few meters.

Plan of the octagonal room.
From Bakker 1999, fig. 30.

The brick walls have a thickness of 0.60. The lower part of the walls shows the core of the wall over a height of 0.40. In the surrounding rooms however the Hadrianic facing continues up to the present floor level. The sides of the octagon measure a little over 20 feet of 0.296 (average length 6.02), created by the openings of the niches, wide passages between the niches, and short wall sections (1.07 long). These short sections partially block the openings of the niches. The diameter of the room, from one corner between the short sections to another, must have been approximately 14.50. In the south part of the south-west niche is a doorway. The jambs show the core of the wall over a height of 0.92. Apparently this was originally a window, later changed into a doorway. In the east part of the south-east niche is an opening with a lintel arch. This opening was blocked, on the inside with brick masonry that is identical to the masonry of the niche, on the outside (in a shop) at a later date (bricks and small tufa blocks). This was either a doorway or a window. In the corner between the two short sections on either end of the wide passage between the south-west and south-east niche is some rubble masonry, probably foundations for columns.

Parallels for this kind of octagonal room can be found in Imperial buildings from the first to the third century AD. They are in the Domus Flavia on the Palatine, in the Piccole Terme and Piazza d'Oro in the Villa Hadriana, and again in Rome in the Baths of Caracalla and of Diocletian.

For the function of the room in the House of the Cistern we have two clues. The missing facing of the lower end of the walls suggests a hypocaust. To the west, below the Forum of the Heroic Statue, the remains of a Hadrianic bath have been found. Was the octagonal room perhaps the vestibule of the bath, slightly heated by the air that had passed through the actual bathing rooms?

In the south part of the building the remains of a Hadrianic arcaded courtyard can be recognized. To the east, along Semita dei Cippi, is a row of shops.

The bakery

In the northern half of the building a bakery was installed, to which some opus latericium seems to be related. On the floor of room 1 are some basalt blocks. In the west part of the tiny room 2 is a basin, widening towards the north. In the east part is a structure looking like a tiny oven: on top of a podium (h. 0.35) was a small cupola (inside diam. 0.60), made of pieces of brick and tufa, opening towards the north (w. of opening 0.38). The area to the south might be called room 3. In the east part is the best-preserved Hadrianic floor-niche. In the niche a large oven was installed. When the oven was built, two walls in the opening of the niche were partly removed. The brick podium of the oven (h.0.98) is protruding from the niche. In the front of the podium is a deep floor-niche or hole. The opening of the oven was towards the west. The first ring of the cupola, made of large tufa blocks, has been preserved (inside diam. west-east 4.00, north-south 4.20). One tufa block has grooves, testifying to a rotating grate on which the bread was placed. There are some basalt blocks on the floor of room 3, and on the floor of rooms 4, 5, and 6. Many basalt blocks and parts of other objects have been piled up in room 6. In the north-west corner of the shop to the east of room 3 is part of a kneading-machine, including part of a hole for the insertion of a blade. In the late 1990's further excavations were carried out in Exedra I,XII,3. Several rooms with floors of basalt blocks were found, some with the imprint of hooves.

A basin, floors of basalt blocks, a large oven, and part of a kneading-machine indicate that a bakery was installed here. Its size and history are obviously problematic. Heres suggests a date in the last quarter of the second century for secondary piers in room 5. The last excavations have shown that the bakery was quite large, and evidently stopped functioning after the building of Exedra I,XII,3, in the middle of the fourth century. The northern part of the building has a total area of roughly 640 square metres. Four pairs of piers on Semita dei Cippi suggest a connection with building V,V,3, that looks like a commercial building.

The water-wheels and cisterns

The south part of the building is in need of further research. In the southern half of the Hadrianic courtyard a large cistern (b) was installed, at two levels. This may have taken place between the end of the second and the fourth century (opus latericium and vittatum). The lower part could contain 80.000 liters. The cistern was supplied by two water-wheels (a). It may well have served the neighbouring Baths of the Forum, and perhaps other buildings as well.