In /r/papertowns you see tons of huge/prominent star forts (otherwise known as trace italienne) surrounding cities in the 16th century. This style of fortification was apparently not only quite effective but also very durable, but you don't see any trace (no pun intended) of their existence on Google Maps. I'm wondering when most of these fortresses disappeared and what happened to all that stone and earthworks. Did they become obsolete and get taken down on purpose, or did they just crumble over time? Obviously most of these cities grew to be much larger later on, so how long were these impressive structures actually intact?

EDIT: I have been made aware that there are pieces of some star forts that are still intact, which is good to know. However, I'm specifically interested in the fate of those star forts that are no longer intact, because it seems bizarre to me that they could be removed from a city without any trace remaining.

At any rate, it seems that there are more surviving medieval castles than star forts, and I would assume that this is due to the fact that the medieval castles tend to be located in more remote areas than star forts, but if someone would like to correct me on that then please go ahead. However, I would still like to know about the process of taking down such prominent and large fortifications.