It is very common, in downtown Lisbon, when doing some escavations to renovate some building foundations to find traces/layers of older civilizations. A famous case was in the 90's when renovating the headquarters of Millenium Bank. The remains were preserved (under the building) and you can actually visit them nowadays[1].
But it was severely devastated by 2 earthquakes. The first was in 1531. The worst was in 1755, an huge tragedy that left marks in European culture (creation of seismology, a bit discussion on the vindication of God within the Enlightenment,...)
Yeah in 1775 it happened during All Saints Day, and I think they still say "Todos os Santos não chegaram"which translates to something like "All saints were not even enough to save us"
[1] https://www.lisbonlux.com/lisbon/nucleo-arqueologico.html