Baiae

This research is focused on one of the most ancient domes of large rise and span built in opus caementicium: the dome of the temple of Diana in Baiae. The main purpose of this paper is to prove that the geometric meridian profile adopted by the Romans for the dome is different from the polycentric profile proposed by Rakob in 1988, which presents some inconsistencies as regards the position of the centres of the upper arcs and the presumed presence of a cusp at the top, not visible at the extrados. To the aim of the research thesis, a recent architectonical survey has been performed and a methodology based on a multi-disciplinary approach has been adopted by critically examining significant aspects related to both the geometry and structural behaviour of the dome: the appropriate choice of the meridian geometric profile, related to historical context, suggestions received from Sassanid constructive traditions and geometric knowledge at the time the dome was built; the Romans’ intuitive and experimentally based understanding of the influence that geometry could have on the mechanical behaviour of a given dome’s profile; and, finally, the adoption of a very small thickness allowed by the opus caementicium constructive techniques, so that the dome can be considered as a first unaware anticipation of the modern membrane theory for thin domes. Results of the architectonic surveys performed up to now, by Rakob in 1988 and recently in 2017, are discussed. Then, after a theoretical investigation on possible profiles of the upper calotte, either circular or parabolic, a statistical regression is undertaken in order to compare theoretical and experimental data of both the surveys. Important considerations on the actual dome springing, and the demonstrated absence of any cuspidal shape at the dome’s key, confirm the Authors’ thesis: the meridian profile is well described by a parabola — the best approximation of a catenary —, which immerses itself in the tambour and continues to be fully contained in it as far as the dome springing. Moreover, mechanical analyses on the structural efficiency of both the polycentric profile proposed by Rakob and the parabolic one thus identified are performed. The analysis confirms that the dome could have been built without the aid of global centring, by demonstrating that the Romans were experimentally aware of the dome’s mechanical behaviour in relation to the various construction phases and the consequent solutions adopted. Finally, the stability of both the overall and partially collapsed structure is examined.

In June 2018, the Nucleo per gli Interventi di Archeologica Subacquea (NIAS) of the Istituto Superiore per la Conservazione ed il Restauro (ISCR), in strict collaboration with the Parco Archeo- logico dei Campi Flegrei, conducted a set of archaeological surveys and conservation works on two floor mosaics located in the area of the archaeological site of Submerged Baiae. One in the thermal baths located immediately north of the so-called “Villa con ingresso a protiro”, the second located slightly south-west of the Punta Epitaffio. Both mosaics are situated within the area under the jurisdiction of the Submerged archaeological park, in a sector where several underwater trails are already accessible by recreational divers and several others are planned to be established in the near future. The activities on two mosaics have been funded by the project BLUEMED - Plan/test/coordinate Underwater Museums, Diving Parks and Knowledge Awareness Centres in order to support sustainable and responsible tourism development and promote Blue growth in coastal areas and islands of the Mediterranean, and co-funded by the European Regional Development Fund. These are part of the ISCR consolidated efforts towards the monitoring, preservation and restoration of the archaeological remains, conducted in the last fifteen years in Submerged Baiae, testing innovative methodologies and technologies for the preservation of the underwater cultural heritage (Project Restaurare sott’acqua).
Possibly dating to the middle imperial age, the first is a bichrome floor mosaic, with black and white tesserae, framed by a monochrome triple band delimitating a representational field with an agonistic sub- ject. Here four male figures are represented, set with black tesserae on a white background. Two of them are athletes who are testing themselves in wrestling, while the other two figures are badly preserved. Holding a branch, one of them could be well identified with the judge/trainer. The portion of the mosaic area brought to the light and completely restored covers a surface area of approximately 12 square meters. It would have been part of a room, perhaps the apodyterium, belonging to one of the two thermal complexes identified along the north-eastern shore of the Baianus lacus.
The second, is a polychrome tessellated mosaic with a geometric decorative scheme, composed by octagons aligned to compose a chessboard and equilateral rhombuses filling the spaces between the octagons. The rhombuses are decorated with floral motifs realized with white, black, red, ochre yellow, pink and turquoise tesserae.
The equilateral rhombuses appear further subdivided by the only colouring of the tesserae into four rect- angular triangles of red, ochre yellow, pink and turquoise. The frame of the mosaic consists of a monochrome quadruple line that frames polychrome rectangular backgrounds repeated cyclically on the perimeter of the mosaic. This polychrome tessellated, in a bad state of preservation – above all due to the disconnections and depressions of the floor level – completely covered an almost square room of 4.30x4.25 m located in an area still little investigated located at about 100 m south-west from the Nymphaeum of Punta Epitaffio. After a brief archaeological overview of the areas of interest, the reflections arising from the analysis of the mosaic floors and the conservative intervention methods adopted will be presented.