The Rosetta Stone was found by French soldiers in 1799, taken by the British in 1801 under the terms of a military surrender, and has been in London ever since.
Egypt has been asking for it back for decades. The British Museum has declined, on grounds that shift with each request: it is better preserved here, it belongs to the world, returning it would set a precedent.
A burglar who steals a painting and later discovers it is a masterpiece is still a burglar.
But the stone is a symbol, and symbols can be a distraction. The repatriation argument is the easy part of this, and it is not the part that did the lasting damage.
Colonialism is usually described as an economic project, the extraction of resources, or a political one, the imposition of European governance. It was both. It was also an epistemological project, and that had two halves which are worth separating because they are not equally repairable.
The first half is the taking. Manuscripts, artefacts, specimens, techniques, and a very great deal of botanical and medical knowledge acquired by asking local practitioners and then publishing without them.
The second half is the destruction of the conditions that produced the knowledge in the first place, and there is nothing to catalogue.
Endowments were appropriated or allowed to lapse. Indigenous institutions were defunded in favour of colonial schools teaching a European curriculum. The language of advancement became the coloniser's, so that ambitious students stopped training in the local scholarly tradition because it led nowhere.
You can send the manuscripts back. You cannot send back the six centuries of continuous practice that would have made someone capable of extending the argument in them.
Colonised peoples were held to have no intellectual history. Not a diminished one, none. That claim did an enormous amount of work: it justified the taking, because objects with no living tradition behind them are better off in a museum; it justified the replacement of local institutions, because there was nothing there to replace; and it justified the extraction, because a people with no history has no claim on the future.
Which puts the Rosetta Stone in its proper place in this book.
It is not mainly an argument about who owns a slab of granodiorite. It is that the same civilisation which spent the twelfth century learning Arabic in Toledo so it could receive what the Islamic world had preserved, spent the nineteenth century removing the material foundations of knowledge from the societies it governed, while explaining that they had never had any.
The chain did not break by accident in this period. It was cut, in a great many places at once, by people who then reported that there had never been a chain.