Here.
Finders-keepers is a basic human behavior. Surely, after several centuries have gone by, a piece of property must be considered lost and unowned.
You thought Rothbard was exaggerating when he called the State "the eternal" but he wasn't. The people to whom the treasure once belonged have been dead and gone for centuries. Even the State which the treasure is imprinted with has long been gone. Its throne has changed hands several times under rulers of varying geographic origin. It is the imagination of the public which melds and unifies all of these unrelated historical particulars into a single entity called "Spain", an entity which is singular, telic and eternal... like some kind of abstract deity.
The long-run consequences of such rulings is also predictable and precisely the opposite of what is intended. Treasure-hunters are less likely to search for treasures which will be costly to find and recover as the prospect of losing them to ancient claims is essentially unbounded. Those who do search for treasures are more likely to destroy the precious metal artifacts (the melt value alone is huge!) or sell them into private, black-market hoardes where their pedigree and authenticity will be lost, depriving all of us of valuable historical knowledge.
But Spain misplaced his (her?) gold a few hundred years ago and now that somebody found it, he is simply requesting for its return like any owner would.
/facepalm
Clayton -
Didn't even have to read beyond the title before i lol'd
American salvage company returns Spanish treasure
And someone thought they were being cute suggesting eternal copyright....
Not to disagree with your overall point Clayton, because I don't, but due to sucession of states it could make legal sense for modern Spain to inherit claims from centuries ago.