Rome's Vittoriano is sinking slowly

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Satellite data reveals millimetre-scale subsidence at Altare della Patria. Rome's Vittoriano monument in Piazza Venezia is sinking slowly, according to a new study, with the north-western side of the landmark subsiding at a rate of around one millimetre per year. The Vittoriano, also known as the Altare della Patria, was built in honour of Vittorio Emanuele II and inaugurated in 1911. Designed by Giuseppe Sacconi, it has housed the Tomb of the Unknown Soldier since 1921 and serves as the principal site for Italy's official state ceremonies. The study was conducted over a 17-year observation period by the applied research firm Nhazca in partnership with Sapienza University of Rome and the National Institute for Environmental Protection and Research (ISPRA). The results revealed non-uniform behaviour: while the northwestern sector of the Vittoriano is subsiding by up to a millimetre per year, the eastern section remains broadly stable. On the perimeter wall overlooking Piazza Venezia, the overall subsidence during the observed period amounts to about five millimetres. Radar images The study analysed more than 300 radar images acquired between 2002 and 2019 by the European ENVISAT satellites and the Italian COSMO-SkyMed constellation. The technique used is known as A-DInSAR - advanced differential radar interferometry - which involves comparing large numbers of radar images of the same point over time in order to measure displacement. This approach allowed the researchers to reconstruct millimetre-scale deformations of the monument without installing any instruments on the building itself. By cross-referencing the satellite data with a geological reconstruction of the subsoil, the researchers identified the cause of the movements. The most unstable areas rest on alluvial terrain, which is more compressible and capable of generating differential foundation settlement. The same phenomenon has been linked to cracks that have appeared on the western face of the building. Satellite technology Alessandro Brunetti, director general of Nhazca, noted the broader significance of the methodology: "For a long time we waited for a crack to become visible before realising something was moving" - Brunetti stated - "Today satellites allow us to see a monument shift by a few tenths of a millimetre per year, reconstruct its history over the past 20 years, and understand why it is moving - without ever touching it. This changes the way we protect heritage: we can intervene before the damage becomes irreversible, across very large areas and at sustainable cost."