In the final chapter, however, there is an insight that relates to ruins, in a section relating to parasites:
"A building's users are also its users-up - its parasites. Think of what happens, say, to a historic cathedral, castle or palace. The visitors wear out carpets and floors, mark the walls, and bore, annoy, insult, manipulate, or otherwise wear down the staff (we will consider the staff to be the monument's auto-immune system). Yet at the same time, the very presence of these tourist-parasites is flattering. They are there to admire. They want to take something of the building's beauty with them. (Sometimes they do this quite literally.) The whole history of Ruinenlust, of ruin worship, could be rewritten as a study in parasitism." (The Monumental Impulse, 182-3)The metaphor is interesting, in that it illustrates the conflict between use and maintenance. If a building has no one to attend to it, it will become a ruin. Having lots of traffic both hastens the destruction and provides (potentially) the resources and impetus to withstand the destruction. The building's users, however, are unlike parasites in that the building only exists to serve the users, and without users the building would disintegrate nonetheless.