Yet another bid is underway to have the Elgin, or Parthenon, Marbles sent back to where they came from. People who think the Parthenon sculptures rightly belong in Athens rather than the British Museum are not, of course, trying to purify the nation of foreign art: in their understanding they are righting old wrongs, campaigning to return the spoils of empire to their proper place.

Yet there is a puzzle here. This emphasis on “repatriation”, a theme that goes beyond the marbles to involve numerous objects ranging from Australian Aboriginal bark art to the Indian Koh-i-Noor diamond, is contemporaneous with the liberal mass migration of our globalised, connected world.

In 2015 there were 244m people living in a different country from where they were born, up 41% on the year 2000. In Europe, migration has become a particularly hot topic. The European Union’s emphasis on freedom of movement combined with the current influx of asylum seekers and other immigrants is causing political upheavals – in the UK, the Brexit debate and its aftermath turned partly on how much immigration the country can and wishes to absorb.

Claims that cultural objects should rightfully be returned to their places of origin have come to prominence at a time when humans are leaving their lands of birth in great numbers. Many settle permanently or indefinitely, blending their cultures into those of their new homes. And at the other end of the spectrum from these migrant settlers, there are the footloose international travellers motivated by sheer cosmopolitan wanderlust. If people so often do not stay in their lands of origin, why care whether objects do?

Who owns what

Part of the answer will often involve beliefs about who are the rightful owners of an object, but this is not a comprehensive answer. After all, some of these possibly rightful owners may themselves be migrants, moving and dispersing around the world and carrying their cultures with them as they go. This is a minor complication when dealing with the lineages of individuals, such as Jews from whom the Nazis confiscated artworks; but the big debates about the ethics of cultural heritage involve objects said to belong to peoples, to cultures, to civilisations.

The role of national governments is therefore a point of some controversy. James Cuno, president of the Getty Trust – the world’s wealthiest art institution – wrote with particular cynicism about “nationalist retentionist” regimes’ use of heritage to legitimise themselves as the successors of earlier rulers. All states seek to forge visions of national identity, and perhaps those which more recently became self-governing nations feel the keenest need.

Yet one sees little retentionism in Greece’s policy on human migration: a member of the Schengen Area, it lost about one person in 50 following the recent financial crisis. Inward and transitory migration have also been high recently, owing to the inflow across the Mediterranean. Similar things can be said of Italy, a country where rules on the export of books are notoriously tight yet is also a state that has seen an exodus of citizens.

Symbolic identity

Here, then, is how we can perhaps make sense of it: states become especially interested in returning significant objects to their places of origin because they have become less interested in borders for human beings. Heritage objects are always important to countries, but more so for countries that increasingly cannot be defined by their populations and the informal culture they share.

This is of course not a total, comprehensive answer: global migration is uneven, and some repatriation claims involve Indigenous peoples within countries, rather than governments of sovereign states. Yet mass migration forces us to ask again for whose culture states can speak. Debates about the rightful fate of cultural heritage tend understandably to look back upon transitions from a time of empires to the age of nation states. Perhaps we find ourselves stumbling into a transition from territories of people to territories defined by symbols and historic artefacts.

Does this make it pointless to campaign to send things back? Maybe not. Symbols can be important, as can the places where things happened – does it erode the meaning of names on a village war memorial if all their descendants are gone? Yet the more people there are who migrate and mingle throughout the modern world, the less possible it will become to think that anything can be set back among the people of its origin.

To have porous borders is to accept the flow of people and their cultural identities across them. While controversy keeps raging over ancient art and which nation’s museums should have it, some newer works are exhibited in appropriate places for our age: inside airports.