A posthole is nothing — a stain in the soil where a wooden post once stood and later rotted away, leaving no artefact at all. Archaeologists read postholes as confidently as they read pottery, because absence, in the right context, carries as much information as presence. A row of evenly spaced postholes is a building's floor plan, written entirely in negative space.
The link rot problem is a preservation problem
Digital preservation is starting to face its own version of the posthole: a citation to a page that no longer exists is a kind of digital postmark, evidence something was once there, structured and important enough to be linked, even though the object itself is gone. Projects like the Internet Archive's Wayback Machine exist for the same reason archaeological survey exists — because absence discovered too late is unrecoverable, and someone has to be capturing the postholes before they fill in.
Format obsolescence as slow decay
A more literal parallel: a file in a format no current software can open is functionally a ruin, present but unreadable, the digital equivalent of an inscription in a script no one alive can translate. Archives that migrate formats proactively, rather than waiting for the obsolescence to become a crisis, are doing conservation, not just storage — a distinction preservationists have understood about physical sites for far longer than IT departments have understood it about file formats.
A ruin isn't a failure to preserve. It's what preservation looks like when nobody was actively doing it.
Every unreadable ZIP file from 2003 is a small, undramatic ruin, and treating it as one is the first step toward not making another.