Spatial planning and architectural innovation in the Roman town of Ocriculum.

The Roman settlement of Ocriculum (Otricoli, TR - Umbria), built on a tufa slope between the Tiber valley to the north and the San Vittore 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 structures are none the less crucial to a thorough analysis of the urban planning of Ocriculum. Two buildings are mutually connected inside the city, even if they were not built at the same time: the bath complex, built in the mid-2nd century AD and restored until the 4th-5th cent. AD, and the underlying culvert, in which the San Vittore still flows, which was certainly built before the baths and most likely alongside the substructures. This artificial terrace, on which the baths lie and under which the channel runs, has been the first human alteration of the slope. The bath complex, although not entirely preserved, features several interesting architectural innovations. Modern technologies were employed alongside traditional methodologies to analyse the two buildings. This allowed not only a 3D reconstruction of these structures, but also a deep knowledge of the urban development and architectural history of Ocriculum. The culvert is part of the earliest attempts to shape the natural landscape for settlement purposes. On the overlying terrace there should have lain not only the bath complex, but also the theatre scene and its porticus post scaenam (both no longer visible). For this reason, the theatre is later than the culvert and not earlier (Hay-Keay-Millet, 2013). Consequently, the close “Great Substructures” belong to the same construction phase of the theatre, because they support the thrust of the upper terrace, on which was most likely found the political and religious centre of Ocriculum. Furthermore, the octagonal hall of the baths and the smaller circular hall (the only preserved rooms of the entire complex) are an important proof of the wealth of this city. They were roofed by a so-called shellshaped dome (consisting of 41 nails) and by a dodecagonal cross-vault, consisting of six larger convex wedges alternating with six smaller ones: it seems to be a hexagonal segmental dome. The first one, built as a pluri-composed cross-vault, surely functioned as a hemispherical dome. It lies on a circular springing, that is connected with the underlying octagonal hall through triangular ashlars, covered with plaster. Both the “shell-shaped” dome and the angular connectors are an innovation and also an unicum in Roman architecture. This allows to identify Ocriculum as a very rich town, inhabited by wealthy people enriched thanks to the trades on the Tiber and the Via Flaminia, but also by famous people like Milone (Cic., Pro Milone, 24, 64) and Pompea Celerina, the rich mother-in-law of Pliny the young (Plin., Ep., I, 4, 1). Furthermore, Ocriculum was seamlessly inhabited even after the collapse of the Roman Empire. The baths have repeatedly been refurbished up to the 4th-5th century: this testifies to the importance of this building for the urban community. In the end, the absence of fortifications could be explained with the identification of this settlement near the port as a monumental detachment of the city on the top of the hill (which was never abandoned).