During wartime, precious historical sites are often caught in the crossfire. Last year, for instance, it was revealed that all six of Syria’s UNESCO World Heritage Sites—among them a Roman amphitheater, a crusader castle, and a 2,000-year-old temple—had been damaged or destroyed during the country’s civil war.

To understand the long-term effects of military conflict on ancient structures, a team of researchers in England headed to a gun range and fired .22-caliber rifles at blocks of stone, Melissa Healy reports for the Los Angeles Times. Their findings, published in the journal Royal Society Open Science, suggest that gunfire can cause networks of tiny fractures beneath the surfaces of ancient stone—even when structures show few signs of external damage.

Before taking aim at their unwitting subjects, researchers sought to recreate the hard shell that forms on stone after centuries of exposure to the elements. The team sourced freshly quarried sandstone from Spain, similar in composition to stones used by ancient builders in the West. Then they applied a preservative called Wacker OH 100 to half of the stone blocks.

Next, the researchers started shooting. They stood about 60 feet away from the blocks and fired four .22-caliber bullets into each. The team then submerged some blocks in a puddle of water, and placed others in a temperature-controlled cabinet to mimic the extreme weather conditions of the Middle East.

The .22-caliber bullets used in the study are effectively peanuts in comparison to the military-grade weapons deployed by armies and insurrectionists, and the blocks that were treated with Wacker OH 100 did not show much damage to their surfaces. But when researchers examined these stones using microscopes, X-rays, and tomographic scanners, they found networks of tiny fractures behind the point of impact.

The authors of the study therefore posit that the weakening of stones hit by military fire “may be far more widespread through the material than previously realized.” Should moisture seep into the cracks behind a stone’s surface, it could accelerate the stone’s deterioration.

While the authors of the study note that “further research is needed to comprehend this rather complex issue,” their findings suggest an unsettling possibility: Even when ancient structures appear to emerge from battle unscathed, they may sustain hidden wounds.