[galfarragem]

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].

[1] https://www.lisbonlux.com/lisbon/nucleo-arqueologico.html

[swimfar]

I found it to be a really interesting tour. I think it's free, as well.