The Geochemical Fingerprint of Tufo Lionato Blocks from the Area Sacra di Largo Argentina: Implications for the Chronology of Volcanic Building Stones in Ancient Rome

Abstract

We use trace element discrimination diagrams to provide a geochemical fingerprint for Tufo Lionato, the volcanic rock most commonly used in the ancient Roman dimension stone technique. Based on the comparison of their geochemical signatures, we identify different rock facies of Tufo Lionato employed since the fourth to third centuries and through the second century bce in the construction of the temples of the Area Sacra di Largo Argentina. These rock facies correspond to two previously identified building stones: Aniene Tuff and Monteverde Tuff, named after their supposed source areas located in the Aniene River Valley and in the homonymous locality of the Tiber River Valley, respectively. However, the results of our study demonstrate previous misidentification of these volcanic rocks in the different construction phases of Temple C, providing a revision of the dating system currently accepted for the diffusion of Tufo Lionato architecture. We show that the Aniene facies has been exploited since the end of the fourth century bce and that it was employed along with Tufo Giallo della Via Tiberina in the podium and staircase of Temple C, whereas observations at Largo Argentina suggest that the ‘Monteverde Tuff’ was only sporadically used in the early phases of the dimension stone construction technique.

Combining geochemistry and petrography to provenance Lionato and Lapis Albanus tuffs used in Roman temples at Sant’Omobono, Rome, Italy

“…Until recent work by Marra et al (), which identified a Portuense facies, archaeologists had recognized only two facies or varieties of the volcanic rock known by the geological name of Tufo Lionato: Monteverde and Anio (Italian Aniene ), after the known ancient extraction areas located in Monteverde on the west bank of the Tiber River, and in several localities along the Anio River, respectively (Jackson & Marra, ; Marra et al, ; Quilici, ). According to the chronological scheme proposed by Lugli (), Monteverde tuff was used from the third century B.C.E., Anio tuff from the mid‐second century.…”

“…Marra et al () have demonstrated that no objective criterion based on macroscopic visual inspection alone is sufficient to identify the provenance of samples of Tufo Lionato. In contrast, using a new method of classification based on the ratio of immobile elements (e.g., Farr et al, ; Marra & D’Ambrosio, ; Marra et al, , ), these authors have shown that four samples of Tufo Lionato, collected at different locations in Monteverde and the nearby area of Portuense, yielded homogeneous Zr/Y versus Nb/Y composition that distinguished them from five samples collected at quarry sites in the Anio valley and on the Capitoline hill.…”

“…Using this geochemical fingerprint to determine the provenance of several samples of building stones from Temples A, B, and C in the so‐called Area Sacra di Largo Argentina, Marra et al () have demonstrated that Tufo Lionato from the Anio valley, rather than Monteverde tuff as reported by Marchetti Longhi () and Lugli (), was widely used in the early construction phase of Temple C, dated to the third century B.C.E. (Coarelli, ).…”

“…Integrating the analysis of the macroscopic lithologic aspect with petrographic observation of thin sections using an optical microscope, Marra et al () have shown that the rock facies cropping out in Monteverde is characterized by a fine grain‐size ash matrix and by a rarity of lithic clast inclusions and loose crystals, which by contrast are abundant and coarser in size in the rock facies occurring along the Anio valley. Moreover, centimeter‐sized carbonate and lava lithic clasts are commonly detected at the macroscopic scale only in the Anio facies.…”

“…; Jackson & Marra, ). For many years archaeologists have attempted in good faith to identify the various varieties of tuff used in ancient Roman construction on the basis of visual examination alone, but recent work on the geochemical composition of those stones has proven the inefficacy and unreliability of visual differentiation (Farr, Marra, & Terrenato, ; Jackson, Marra, Hay, Cawood, & Winkler, ; Marra & D’Ambrosio, ; Marra, D'Ambrosio, Gaeta, & Mattei, ). Trace element features of the Lazio tuffs, however, provide accurate and reliable identification criteria to discriminate eruptive products and their source areas (e.g., Lustrino, Duggen, & Rosenberg, ; Peccerillo, ).…”