The Historic Centre of Urbino, UNESCO World Heritage (Marche Region, Italy): an Urban-Geological Itinerary Across the Building and Ornamental Stones

Abstract

The local and extra-regional (national and transnational) stones mainly used as building and ornamental materials in the historic centre of Urbino (UNESCO World Heritage List) were unravelled through a detailed geological and petrographic study. The types of building stones used in the past for the development of an urban centre were mostly affected by the availability of suitable geomaterials in the surrounding areas. For this reason, the stones found in the historical buildings of Urbino generally come from the local sedimentary formations (mostly limestones) belonging to the Umbria–Marche–Romagna Succession Auct., which crops out in the Northern Marche Apennines. Only some ornamental highly prized stones used for monuments and decorations come from both extra-regional Italian areas (Alps, other sectors of the Northern Apennines) and foreign countries (France, Egypt). A brief description of the Northern Marche geology was also reported to exactly match the local provenance of the stones, so highlighting the relationship between the territory and the architecture of Urbino. Because of obvious conservation reasons, no samples were collected from buildings or monuments and only autoptic observations, together with a detailed historical and bibliographic research, were carried out to identify the different materials and the provenance areas. Besides the availability of the local sedimentary rocks, we emphasised how the choice of the building and ornamental stones could have been also influenced by the historic period and artistic style, aesthetic features, economic and social importance of the building and/or monument and the relationship to some distinguished personality (e.g., Pope Clemente XI). An open-air stone itinerary across significant places (10 stops and additional sites and monuments in the urban area) is finally proposed for the best fruition of the geological and cultural heritage of Urbino, also aimed at geotourism development.

Geological Insights on the Calcareous Tufas (Pietra Spugna) Used as Building and Ornamental Stones in the UNESCO Historical Centre of Urbino (Marche Region, Italy)

“…Other samples (TRU1, TRU2, TRU3, TRU5, and TRU7; Figure 3) are all ashlars originally installed in Roman times and reused, between the 14th and 16th centuries, mostly at the base of some younger historical buildings and on the external walls of the Fortezza Albornoz. The reuse of these spongy stones through time is highlighted by the fact that, independently from the period of installation, these stone lithotypes are all characterized by the size extensively characterizing the Roman period (59 × 59 or 59 × 74 cm) to build the defensive dry-stone walls (opus quadratum; [8]). TRU9 and TRU10, come from portals of two important oratories: Oratorio delle Grotte (Figure 4a-c) and Oratorio della Morte (Figure 4d,e), both decorated in the 17th century AD and attributed to the sculptor Bartolomeo Ammanati [29].…”

“…The measurements carried out on the calcareous tufas show a Qua ranging from 33.4 to 45 MPa (Table 2) which can be considered values of moderate-strength stone [33]. Some physical features of calcareous tufas coming from both building stones and outcrops along the Metauro Valley (Canavaccio locality), reported by [8,10], show a dry unit weight (γd) between 1.14 and 1.68 Mg/m 3 ; a specific gravity (γs) of 2.69 Mg/m 3 ; and a porosity (n) ranging between 37 to 57%. Table 2.…”

“…By contrast, it seems to be a calcareous tufa stricto sensu [5,6] representing freshwater rocks deposited by chemical precipitation from low-temperature calcium-bicarbonate-rich waters under subaerial conditions in a large variety of continental depositional and diagenetic environments [7]. Ornamental and building stones made of these calcareous tufas were considered in the open-air stone itinerary across the historical centre of Urbino [8] addressed to geotourism and the best fruition of the geological and cultural heritage of the UNESCO World Heritage Site itself. In the present paper, we are going to focus, for the first time, on the geological origin of these calcareous tufas used in the historical centre of Urbino, also contributing to the stone heritage of the UNESCO site.…”

“…As recently pointed out by [9] comparing calcarenites and calcareos tufas, «the conservation and restoration of cultural heritage must be based not only on the monument and territory history but also on the deep knowledge of the materials». In this way, the conservation of the calcareous tufas of the Urbino historical center cannot be considered, in toto, in the same way as the degradation processes of other carbonate stones (limestones with vacuolar structures, calcarenites, and hydrothermal travertines stricto sensu) used as building stones in the UNESCO site [8].…”

Historical Use of Travertine in the Tuscan Architecture (Italy)

“…In ancient Rome, travertine was the stone of monumental buildings (bridges, triumphal arches, theatres and amphitheatres, arcades, tombs façades) and flooring, but it was also used in private buildings [11]. In the Middle Ages, it was the monumental building material of Ascoli Piceno, Perugia, Ancona, Rieti, in relation to a local extraction [12]. Travertine then became the stone of the Roman Baroque and rationalist architecture, significant examples of which are the University City of Piacentini and the E.U.R complex (Universal Exposition of 1942) [13,14].…”