Archaeologists and physicists both covet ancient Roman lead—for very different reasons. Old lead is pure, dense and much less radioactive than the newly mined metal, so it makes ideal shielding for sensitive physics experiments. But it also has historical significance—and many archaeologists object to melting down 2,000-year-old ingots.

“Are these experiments important enough to destroy parts of our past, to discover something about our future?” asks Elena Perez-Alvaro, an archaeology graduate student at the University of Birmingham in England, who wrote a paper on the dilemmas involved in the journal Rosetta.

Romans once used the lead to make coins, pipes, construction materials and weapons. Today private companies collect it from shipwreck sites and pass it on to customers—many of whom are physicists. “We may lose all ancient Roman lead—and therefore the information about ancient technology, shipping, trade, et cetera, it can offer—if its use for this kind of purpose becomes widespread,” says University of Birmingham archaeologist John Carman.

Physicists argue that using the metal is prudent in key applications, such as in pursuit of dark matter, the material theorized to make up more than one quarter of the universe's mass. “None of us takes it casually—you don't want historical artifacts to be destroyed unnecessarily,” says physicist Blas Cabrera of Stanford University. Cabrera is the spokesperson of the Super Cryogenic Dark Matter Search in Minnesota, which uses the lead for shielding its detector.

And in physics, ancient lead can help solve mysteries that long predate the Romans. “These experiments can reveal some of the most fundamental properties of the universe and answer questions such as what are we and where we come from,” says physicist Fernando Gonzalez-Zalba of the University of Cambridge. “I think it's worth it.”