Seismic vulnerability assessment of the triumphal arch of Caracalla in Volubilis (Morocco): past events and provisions for the future

The triumphal arch of Caracalla in the Roman archaeological site of Volubilis dates back to 216 AD. It was built in a strategic position at the intersection of the main roads leading to the Forum, the decumanus maximus to the east and the roads from Porte à trios baies to the west, that almost certainly was the main gate to the city. The current arrangement of the monument is the result of a restoration intervention carried out in the 1930s by French restorers. Some ancient photos witness that the monument was just a ruin in 1915, when Chatelain carried out the former archaeological excavations and, as a consequence, that it was totally rebuilt. In fact, the monument suffered wide damages provoked by the 1755 Lisbon earthquake, that affected also Morocco, which almost completely destroyed it. By means of the drawings made by the travelers Henry Boyde and John Windus, that retraced the monument thirty years before the earthquake, the original configuration of the monument can be observed and the timeline of events can be reconstructed. In this paper, the timeline of the seismic events that affected the triumphal arch is reconstructed and investigated by means of a structural analysis based on a rigid-block model. Finally, with the purpose of preventing future damage, the seismic vulnerability level of the construction is assessed with reference to its current configuration.