Why old port defenses survive beneath newer buildings

Will more historic port defenses be found partially intact beneath later buildings?

Probably, because good harbors and crossing points remain useful, so settlements and later infrastructure repeatedly grow over the same strategic sites.

Ports resemble river crossings because geography keeps channeling activity through the same place even as the settlement above it changes. That continuity makes buried or incorporated defenses plausible, since later builders often reuse foundations and strategic ground rather than abandon a good harbor.