Engineers trying to warn people 10,000 years from now about buried nuclear waste realised that no language could be trusted to last that long. So they imagined warnings that would not depend on words alone: fields of jagged concrete thorns, hostile earthworks and monuments designed to feel dangerous before they were understood. The message they wanted to send was almost anti-monumental: this is not a place of honour, and nothing valued is buried here.

Engineers trying to warn people 10,000 years from now about buried nuclear waste realised that no language could be trusted to last that long. So they imagined warnings that would not depend on words alone: fields of jagged concrete thorns, hostile earthworks and monuments designed to feel dangerous before they were understood. The message they wanted to send was almost anti-monumental: this is not a place of honour, and nothing valued is buried here.

The problem was not how to write a warning sign. It was how to write one for people 10,000 years from now, after every language on it may have changed beyond recognition. That was the strange design problem behind one of the most discussed documents in nuclear-waste history: the 1993 Sandia National Laboratories report Expert Judgment on Markers to Deter Inadvertent Human Intrusion into the Waste Isolation Pilot Plant. The report was prepared fo…