The fortifications around San Juan are remnants from when the Spanish colonized the Island. The walls have stood for hundreds of years against the effects of nature and multiple sieges, and consist of a multitude of different sites and miles of walls.
The NPS wanted to stabilize and repair the walls after they have suffered from years of wear. Due to the complex nature of the walls, having been repaired multiple times with conflicted materials and techniques, the preservation of the wall proved a large challenge.
The NPS decided to declare all the fortifications a singular site and to study the materials to better intervene and to be better able to repair them.
This is one of the few examples that takes place in Puerto Rico. It is also used worldwide as an example of how to repair old resources and how to use modern technology to understand them.