They used to be built for centuries

Your statement "They used to be built for centuries" seems to refer to structures or monuments that were designed to endure for a long time, perhaps referring to ancient buildings, castles, cathedrals, or other architectural feats from history. Many of these structures were designed with durability and longevity in mind, utilizing materials and techniques that would allow them to withstand the test of time. Could you provide more context or specify what you are referring to? That way, I can offer more detailed information or insights.