The foundational principle upon which the entire law of occupation is based is the principle of ‘inalienability of sovereignty’ through unilateral action of a foreign power.

Accordingly, when a state establishes effective control over foreign territory, its international legal status is conceived to be that of a ‘trustee’ who exercises only ‘temporary managerial’ powers until the occupation ends.

The occupant serves only as ‘administrator’ and ‘usufructuary’ of public monuments belonging to the people of the occupied state/polity.

It must safeguard these public monuments, and administer them in accordance with the rules of ‘usufruct’, avoiding wasteful or negligent destruction of their capital value.

So, an occupying colonial power may not permit a person to lawfully detach/remove any part of the whole, and thereby appropriate the fragment.

Thus, removal of any part of a public monument, i.e. by hacking off a fragment, e.g. part of a ‘frieze’ adorning the monument, is ipso facto unlawful under international law. It must therefore be returned for re-unification with the monument. QED.