In the quest to build better for the future, some are looking for answers in the long-ago past.

Ancient builders across the world created structures that are still standing today, thousands of years later B次元官网网址� from Roman engineers who poured thick concrete sea barriers, to Maya masons who crafted plaster sculptures to their gods, to Chinese builders who raised walls against invaders.

Yet scores of more recent structures are already staring down their expiration dates: The concrete that makes up much of our modern world has a lifespan of around 50 to 100 years.

A growing number of scientists have been studying materials from long-ago eras B次元官网网址� chipping off chunks of buildings, poring over historical texts, mixing up copycat recipes B次元官网网址� hoping to uncover how theyB次元官网网址檝e held up for millennia.

This reverse engineering has turned up a surprising list of ingredients that were mixed into old buildings B次元官网网址� materials such as tree bark, volcanic ash, rice, beer and even urine. These unexpected add-ins could be key some pretty impressive properties, like the ability to get stronger over time and B次元官网网址渉ealB次元官网网址� cracks when they form.

Figuring out how to copy those features could have real impacts today: While our modern concrete has the strength to hold up massive skyscrapers and heavy infrastructure, it canB次元官网网址檛 compete with the endurance of these ancient materials.

And with the rising threats of climate change, thereB次元官网网址檚 a growing call to make construction more sustainable. A estimates that the built environment is responsible for more than a third of global CO2 emissions B次元官网网址� and cement production alone makes up more than 7% of those emissions.

B次元官网网址淚f you improve the properties of the material by using B次元官网网址� traditional recipes from Maya people or the ancient Chinese, you can produce material that can be used in modern construction in a much more sustainable way,B次元官网网址� said Carlos Rodriguez-Navarro, a cultural heritage researcher at SpainB次元官网网址檚 University of Granada.

Is ancient Roman concrete better than todayB次元官网网址檚?

Many researchers have turned to the Romans for inspiration. Starting around 200 BCE, the architects of the Roman Empire were building impressive concrete structures that have stood the test of time B次元官网网址� from the soaring dome of the Pantheon to the sturdy aqueducts that still carry water today.

Even in harbors, where seawater has been battering structures for ages, youB次元官网网址檒l find concrete B次元官网网址渂asically the way it was when it was poured 2,000 years ago,B次元官网网址� said John Oleson, an archaeologist at the University of Victoria in Canada.

Most modern concrete starts with Portland cement, a powder made by heating limestone and clay to super-high temperatures and grinding them up. That cement is mixed with water to create a chemically reactive paste. Then, chunks of material like rock and gravel are added, and the cement paste binds them into a concrete mass.

According to records from ancient architects like Vitruvius, the Roman process was similar. The ancient builders mixed materials like burnt limestone and volcanic sand with water and gravel, creating chemical reactions to bind everything together.

Now, scientists think theyB次元官网网址檝e found a key reason why some Roman concrete has held up structures for thousands of years: The ancient material has an unusual power to repair itself. Exactly how is not yet clear, but scientists are starting to find clues.

In a , Admir Masic, a civil and environmental engineer at the Massachusetts Institute of Technology, proposed that this power comes from chunks of lime that are studded throughout the Roman material instead of being mixed in evenly. Researchers used to think these chunks were a sign that the Romans werenB次元官网网址檛 mixing up their materials well enough.

Instead, after analyzing concrete samples from Privernum B次元官网网址� an ancient city outside of Rome B次元官网网址� the scientists found that the chunks could fuel the materialB次元官网网址檚 B次元官网网址渟elf-healingB次元官网网址� abilities. When cracks form, water is able to seep into the concrete, Masic explained. That water activates the leftover pockets of lime, sparking up new chemical reactions that can fill in the damaged sections.

Marie Jackson, a geologist at the University of Utah, has a different take. has found that the key could be in the specific volcanic materials used by the Romans.

The builders would gather volcanic rocks left behind after eruptions to mix into their concrete. This naturally reactive material changes over time as it interacts with the elements, Jackson said, allowing it to seal cracks that develop.

The ability to keep adapting over time B次元官网网址渋s truly the genius of the material,B次元官网网址� Jackson said. B次元官网网址淭he concrete was so well designed that it sustains itself.B次元官网网址�

Using tree juice to make sculptures as strong as seashells

At Copan, a Maya site in Honduras, intricate lime sculptures and temples remain intact even after more than 1,000 years exposed to a hot, humid environment. And according to a , the secret to these structuresB次元官网网址� longevity might lie in the trees that sprout among them.

Researchers here had a living link to the structuresB次元官网网址� creators: They met with local masons in Honduras who traced their lineage all the way back to the Mayan builders, explained Rodriguez-Navarro, who worked on the study.

The masons suggested using extracts from local chukum and jiote trees in the lime mix. When researchers tested out the recipe B次元官网网址� collecting bark, putting the chunks in water and adding the resulting tree B次元官网网址渏uiceB次元官网网址� into the material B次元官网网址� they found the resulting plaster was especially durable against physical and chemical damage.

When scientists zoomed in, they saw that bits of organic material from the tree juice got incorporated into the plasterB次元官网网址檚 molecular structure. In this way, the Mayan plaster was able to mimic sturdy natural structures like seashells and sea urchin spines B次元官网网址� and borrow some of their toughness, Rodriguez-Navarro said.

Studies have found all kinds of natural materials mixed into structures from long ago: fruit extracts, milk, cheese curd, beer, even dung and urine. The mortar that holds together some of ChinaB次元官网网址檚 most famous structures B次元官网网址� including the Great Wall and the Forbidden City B次元官网网址� includes .

Luck or skill?

Some of these ancient builders might have just gotten lucky, said Cecilia Pesce, a materials scientist at the University of Sheffield in England. TheyB次元官网网址檇 toss just about anything into their mixes, as long as it was cheap and available B次元官网网址� and the ones that didnB次元官网网址檛 work out have long since collapsed.

B次元官网网址淭hey would put all sorts of things in construction,B次元官网网址� Pesce said. B次元官网网址淎nd now, we only have the buildings that survived. So itB次元官网网址檚 like a natural selection process.B次元官网网址�

But some materials seem to show more intention B次元官网网址� like in India, where builders crafted blends of local materials to produce different properties, said Thirumalini Selvaraj, a civil engineer and professor at IndiaB次元官网网址檚 Vellore Institute of Technology.

According to SelvarajB次元官网网址檚 research, in humid areas of India, builders used local herbs that help structures deal with moisture. Along the coast, they added jaggery, an unrefined sugar, which can help protect from salt damage. And in areas with higher earthquake risks, they used super-light B次元官网网址渇loating bricksB次元官网网址� made with rice husks.

B次元官网网址淭hey know the region, they know the soil condition, they know the climate,B次元官网网址� Selvaraj said. B次元官网网址淪o they engineer a material according to this.B次元官网网址�

Ancient Roman B次元官网网址� skyscrapers?

TodayB次元官网网址檚 builders canB次元官网网址檛 just copy the ancient recipes. Even though Roman concrete lasted a long time, it couldnB次元官网网址檛 hold up heavy loads: B次元官网网址淵ou couldnB次元官网网址檛 build a modern skyscraper with Roman concrete,B次元官网网址� Oleson said. B次元官网网址淚t would collapse when you got to the third story.B次元官网网址�

Instead, researchers are trying to take some of the ancient materialB次元官网网址檚 specialties and add them into modern mixes. Masic is part of a startup that is trying to build new projects using Roman-inspired, B次元官网网址渟elf-healingB次元官网网址� concrete. And Jackson is working with the Army Corps of Engineers to design concrete structures that can hold up well in seawater B次元官网网址� like the ones in Roman ports B次元官网网址� to help protect coastlines from sea level rise.

We donB次元官网网址檛 need to make things last quite as long as the Romans did to have an impact, Masic said. If we add 50 or 100 years to concreteB次元官网网址檚 lifespan, B次元官网网址渨e will require less demolition, less maintenance and less material in the long run.B次元官网网址�

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical InstituteB次元官网网址檚 Science and Educational Media Group. The AP is solely responsible for all content.

Maddie Burakoff, The Associated Press