Desertification can wear down ancient ruins or hide them under dunes—leaving researchers scrambling to keep track of where they’re buried.

By Charlie Metcalfe

The Nizari garrison at Gird Castle resisted the Mongol horde of Hulagu Khan for 17 years before surrendering in December 1270. The fortress rose 300 meters above the surrounding plains of present-day eastern Iran, with three rings of fortifications enclosing its base. But dwindling supplies and an outbreak of cholera forced the defenders to abandon their posts after one of the longest sieges in medieval history.

Eight hundred years later, the remaining fortifications at Gird Castle face the onslaught of a new invader: sand. For the past three months, Bijan Rouhani, an archaeologist at the University of Oxford, has been monitoring about 700 sites in Iran’s Sistan region using satellite imagery. His comparison of US intelligence photos taken in 1977 and Google Earth’s most recent images of the area shows the advance of vast dunes that now almost bury the fortress at Gird.

This summer, drought has revealed a number of previously hidden archaeological sites as low water levels have allowed archaeologists to access historic ruins in Spain, Iraq, and China. But just as climate change giveth, so it taketh away: Rising heat is damaging some ancient sites and spurring desertification that is burying others, Gird Castle among them. It is a growing problem with few proven solutions.

“We can see many other sites from the Bronze Age to the Islamic periods in the area, as well as ancient rivers and canals,” says Rouhani. “Most of these sites are now buried under sand and impacted by the 120-day sand wind every year.”

The ancient city of Zahedan Kohneh has suffered the same fate as Gird Castle. It was Sistan’s capital when Gird fell to the Mongols and was once one of the largest cities in Iran—today it is draped in a growing garment of sand. Archaeologists monitoring sites in other regions, countries, and continents report similar stories. Ahmed Mutasim Abdalla Mahmoud, a researcher specializing in sand movement at the University of Nottingham, says sand poses the biggest threat to Sudan’s Nubian pyramids, built around 4,500 years ago. He warns that the 200 pyramids at El Kurru, Jebel Barkal, and Meroe on the Nile River could soon disappear beneath sand.

“The threat has been exacerbated by climate change, which has made the land more arid and sandstorms more frequent,” he writes on the Conversation. “Moving sands can engulf entire houses in rural Sudan, and cover fields, irrigation canals, and riverbanks.”

Mahmoud and other archaeologists concede that people in these areas have struggled with encroaching sand dunes for millennia. But climate scientists leave no doubt that human activity is increasing the speed of desertification. Some forecast that at the current rate, emissions will lead the Middle East and North Africa region to heat by 4 degrees Celsius within the next 30 years. These rising temperatures cause drought, and drought transforms land into desert. Over two-thirds of Iran’s land mass now shows “high” or “very high” susceptibility to desertification.

Some archaeologists suggest that sand inundation could protect sites from looters and exposure to harsh weather. Many sites that are already buried have survived for millennia because of this. But Michael Fradley, an archaeologist specializing in the Arabian Peninsula at the University of Oxford, believes rapid changes in the environment will cause more damage to sites than any supposed benefits that might help save them. “The stability that has maintained these sites for millennia is changing,” he says. “Even if a site isn’t completely covered, the constant changing starts to break structures apart, whether it be a single brick or an entire settlement.”

Sites beyond the reach of advancing dunes can also still suffer the effects of severe drought. Drought decreases the amount of water flowing down rivers, and this reduces the sediment supplied to estuaries, where it would otherwise build up along the coast and act as a buffer against erosion. Coastal sites lose their protection in this way.

A group of Iranian and French researchers studied Iran’s ancient port city of Siraf in 2018 to measure the consequences of this effect. Siraf acted as an important link between the Islamic world and Eastern lands like China as far back as 1,800 years ago. Later it became an enormous trading hub, where merchants also brought gemstones, ivory, ebony, paper, sandalwood, drugs, pearls, and spices from Africa and India. The researchers discovered that the waters of the Persian Gulf were grinding almost half of the coastline at Siraf into the sea. This had already led to “widespread and archaeologically significant damage” to its old city walls, the potters’ quarter, great mosque, and ancient bazaar. The team posited the reduction in coastal sediment supply as a principal reason. Nick Marriner, a researcher from the University of France-Comté who worked on the project, says this year’s severe droughts have accelerated the erosion.

Coastal erosion threatens archaeological sites on every continent. Sixty percent of Africa’s 284 coastal sites of “outstanding universal value” could be at risk from a one-in-100-year extreme coastal event by 2050. And 42 of Europe’s Unesco World Heritage Sites in low-lying coastal regions of the Mediterranean are at risk of erosion. “Current climate change projections, coupled with human impacts, mean that the future is bleak for the ancient remains of many archaeologically rich coastal sites,” Marriner says.

Archaeologists have few tools to prevent the destruction resulting from drought; budgets already strain to protect the most important sites. Building a sea wall that might save coastal sites like the ancient port at Siraf would cost at least $400,000 per kilometer. That’s out of the question, Marriner says.

The most effective protection measures would be those that prevent drought in the first place. This demands first an immediate reduction in the human greenhouse gas emissions that warm the Earth and stimulate desertification. Governments must also develop more sustainable water policies and settle disputes over water with their neighbors to lessen the impact of drought. Iraq’s government, for example, claims that immense damming projects in Turkey and Iran will reduce water flowing down the Tigris and Euphrates rivers by 60 percent in the next 14 years. Jaafar Jotheri, a professor of geoarchaeology at the University of Al-Qadisiyah in Iraq, says this forces farmers to exploit salty underground reservoirs to spray their crops. Wind then blows the salt onto Iraq’s multitude of archaeological sites, some as old as 5,000 years, and permeates their semi-organic mud bricks. The bricks crumble. Jotheri says the salt can invade foundations by capillary action alone.

“We will lose our archaeological sites 100 percent,” he says. “I mean totally lose them because they will be covered by sand. The rest will be destroyed by the wind, temperature, and salt.”

Archaeologists can try to convince governments to consider physical heritage in their environmental policies. People, however, must come first. Drought has already forced Iranians to abandon 1,700 villages in South Khorasan, the region on Sistan’s northern border. Those may soon join the ruins of ancient civilizations beneath the dunes of sand.

For now, researchers can focus only on documenting as many affected sites as possible. Both Rouhani and Fradley work for the Endangered Archaeology in the Middle East and North Africa project at Oxford, which has developed a public database of over 333,000 sites across 20 countries and encourages other archaeologists to contribute their own data. Sand might entomb even the tallest spires and citadels, but thanks to the project’s work, we’ll at least know where to dig.