Spatial Planning and Architectural Innovation in the Roman Town of Ocriculum.
Keywords:architectural innovation, culvert, Ocriculum, Thermae, urban planning
The Roman settlement of Ocriculum (Otricoli, TR - Umbria), built on a tufa slope between the Tiber’s valley to the north and the San Vittore stream valley to the south, was established on massive substructures, which allowed the exploitation of a larger area. Albeit being relatively neglected by modern scholarship, these preliminary constructions are none the less crucial to a thorough analysis of the urban planning of Ocriculum.
There are two buildings mutually linked inside the city, although built not at the same time: the bath complex, erected in the middle of the II cent. AD and restored until IV-V cent. AD, and the underlying culvert in which still flows the San Vittore stream, built surely before the baths and as much certainly together with all the urban substructures. This artificial terrace, on which the baths tand and under which the channel runs, has been the first regularisation of the slope, starting indeed from the little but deep valley of the San Vittore stream. The bath complex, additionally, although not entirely preserved, features several interesting architectural innovations.
Thanks to modern digital technologies but even to traditional methods, it was possible to study in a greater detail the aforementioned buildings. This allowed to rebuild by 3D-modeling programs these structures and to deepen knowledge about the urban planning and history of Ocriculum, on one side, and about its architectural influences, on the other side.
The culvert, indeed, belongs to the first regularisation work of the settlement: on the overlying terrace should stand not only the bath complex, but also the theatre scene and its rear porticus (both no longer visible). Thus, also the theatre is later than the culvert and not previous (Hay-Keay-Millet 2013). Consequently, the near “Great Substructures” belong to the same construction period of the theatre, because they together support the thrust of the upper terrace, on which, most probably, there was the political and religious centre of Ocriculum.
Furthermore, the octagonal hall of the baths and the smaller round one (the only two preserved of the entire complex) are an important proof of the richness of this city. They were roofed by a segmental dome consisted of 41 nails (indeed it is so called “shell-shaped”) and by a dodecagonal cross-vault, consisted of six larger convex wedges alternate with other six smaller ones: in this way it seems to be a hexagonal segmental dome. The first one, built as pluri-composed cross-vault, surely had to work as hemispherical dome: indeed, it lies on a circular springing, that is linked with the underlying octagonal hall through masonry convex triangles, covered with plaster. Both the “shell-shaped” dome and the angular links are an innovation and also an unicum in Roman architectural context.
This allows to identify Ocriculum as a very rich town, inhabited by wealthy people enriched certainly thanks to the trades on the Tiber and the Via Flaminia, but also thanks to the imperial frequentations about which the ancient authors talk. Furthermore we have to consider that this town near the Tiber’s banks kept to be occupied during Barbarian Invasions and further to the end of Roman Empire. The baths mostly kept to be restored until IV-V century: this testifies the importance of this building for the citizenry. In the end, the absence of defensive walls could be explained with the identification of this settlement near the port as a monumental detachment of the city, never abandoned, on the top of the hill.