Every now and again, real-life archaeology sounds a little like an Indiana Jones movie. Allied bombers dropped 165 bombs on the ancient Roman city of Pompeii, and at least seven of them may still lie buried and unexploded amid the ruins. The bombs, scattered over 22 hectares of the site that haven’t been surveyed or excavated, don’t pose a danger to tourists, but they’re a challenge for future excavations.

Bombing the ruins

The eruption of Mt. Vesuvius entombed the city of Pompeii in ash in 79 CE. Fire rained down on the ruined city again in August 1943, when US and British bombers began pounding German encampments and supply lines in southern Italy. The US 5th Army had launched Operation Avalanche, a campaign to seize the nearby port of Naples, and the 12th Air Force Bomber Command dropped ordnance on anything that could support Nazi forces in the area.

Naples was the second-most heavily bombed city in Italy. In 1943, the city weathered 181 bombing raids—nine of which struck the ruins of Pompeii. “Those were the months in which the anti-aircraft alarm sounded in Naples every day,” reported Il Fatto Quotidiano. Between 20,000 and 25,000 people died. In the middle of it all, Archaeological Superintendent Amedeo Maiuri and his colleagues moved several statues and artifacts from Pompeii underground for safekeeping.

But why would the Allies bother bombing a city that had been destroyed by a volcano 1,800 years earlier? In a November 1943 story describing the damage (with a level of detail that would probably be considered an operational security violation today), the Times of London reported that “the Germans were encamped on the site, and Allied aircraft were obliged to treat it as a military objective.”

In particular, the Allied chain of command had received reports that a German force—maybe even a whole division—had camped among the ruins, complete with anti-aircraft guns and a command post in a hotel nearby. According to Maiuri, writing in the American Journal of Archaeology in 1944, the command post was real, but the encamped German division was just a rumor. The Nazis had just two anti-aircraft guns, both well outside Pompeii’s walls, and a few trucks parked nearby.

Deadly time capsules

Based on Allied maps and reports now housed in Italian government archives, 165 bombs fell on Pompeii in 1943. The bombs damaged, and in some cases totally destroyed, several of the streets and buildings archaeologists had already unearthed from the thick layer of ash that entombed the city. (Archaeologists restored or rebuilt some of those structures after the war.)

But between 12 and 16 of those bombs may have plummeted to Earth, digging themselves into the ash and sediment that covers the ruins without exploding. That’s based on the assumption that roughly 8% to 10% of bombs dropped during WWII struck without exploding, as the Order of Engineers of Mantua estimated last year. Several bombs have been found and defused over the years, so Il Fatto Quotidiano claims that seven to 10 may still be waiting in the unexplored sections of Pompeii.

An exploded bomb may be a harmless dud, but it could also just be waiting for someone to jostle it the wrong way.

Meter by meter

Several unexploded bombs have turned up over the years in the 44 hectares of Pompeii that archaeologists have surveyed. An English pilot found one lodged in the ground near an ancient Roman house, called the House of Epigrams because its walls boasted frescoes with Greek writing beneath them. The most recent one turned up in 2017. Archaeologist Antonio De Simone told Il Fatto Quotidiano that his excavation ran across two bombs in 1986. One of them had detonated, but one remained “beautifully intact”—and potentially deadly.

Left in the ground, unexploded bombs obviously pose a threat to the otherwise well-preserved ancient city—and to the archaeologists, like De Simone, who might inadvertently dig them up. But dealing with them is a slow, costly, process. Tools like magnetometers, which look for changes in magnetic fields that might reveal the presence of iron and other metals, are essential.

“We proceed like this, meter by meter: first the analysis, then the drilling. Only then will we be able to save the Roman remains and eliminate the bombs,” engineer Paulo Orabona, who removes unexploded bombs from construction and excavation sites, told Il Fatto Quotidiano. The Italian military is responsible for finding and defusing unexploded bombs at Pompeii.

But the process of removing the bombs once they’ve been found doesn’t always fit well with archaeologists’ ideas about careful excavation. “Archaeological inspections and bomb reclamation follow different techniques. Those who search and defuse the devices proceed with breaking the ground, a procedure much more invasive than what we archaeologists use,” De Simone told Il Fatto Quotidiano.

A modern problem in an ancient city

The bombs are a problem the ancient city of Pompeii shares with the rest of modern Italy. Allied aircraft dropped about a million bombs on the country between 1943 and 1945. Most of those would have exploded on impact, and they’re no longer a threat today. That deadly work is done. But if the Order of Engineers’ estimate is accurate, then about 80,000 to 100,000 unexploded bombs littered the Italian landscape after the war.

Efforts to clean up bombs, artillery shells, land mines, grenades, and other unexploded ordnance in Italy started in 1946. The following year, the US government gave Italy all the information it had gleaned about bomb locations from Allied forces’ reports during the war. According to Il Fatto Quotidiano, military engineers in Italy unofficially estimate that they’ve found and defused 60% of the unexploded bombs from World War II so far. The Ministry of Defense says it still finds thousands of undetonated, potentially lethal leftovers from the war every year—2012’s figure was 9,177 pieces of ordnance, including 81 bombs dropped from aircraft.

Italy’s story isn’t unique. In many countries around the world, bombs and land mines continue to kill and injure people decades after the end of conflict. As at Pompeii, governments and non-governmental organizations around the world must reckon with the deadly time capsules left behind.