what does "little remains aboveground from the time of the etrusacans, whose exact origin is unknown' means in the reading

The Etruscan civilization is the name given to a civilization of ancient Italy which was considered to be powerful and wealthy. It developed in the area which is currently known as Tuscany. What the author is trying to say is that it is very difficult to track the origins of this civilization, due to the fact that there are very few standing constructions that can be considered to have been built by them. The majority of them have fallen down across time or are underground.