It's not usually time based. Some countries have laws like NAGPRA in the US that protect the graves of specific groups regardless of age but otherwise it's a ve

It's not usually time based. Some countries have laws like NAGPRA in the US that protect the graves of specific groups regardless of age but otherwise it's a very fuzzy line to draw. The two extremes are: - If the polity that the person belonged to still exists, then it's a very sensitive issue - like US civil war graves. Likewise if there is a clear cultural continuity - for example France's first republic to the modern era. Both of which are themselves fuzzy criteria but largely fall into the desecration camp (although there are exceptions, not all cultures view it as taboo when done for scientific/historical purposes). - If neither the polity nor the culture - often delineated by writing system or state apparatus or other semi-arbitrary line - still exist then the grave is pretty much fair game ethically speaking (legally it depends on the jurisdiction). That fuzziness in the middle is very problematic but modern archaeologists have a whole process for reaching out to governments and getting consent from any descendant communities if applicable, and then coming up with an ethical plan to rebury/preserve the remains afterwards. IME the majority of such communities are very cooperative because it helps them answer questions about their past.