The Roman Colosseum is a giant, oval amphitheater built almost two thousand years ago. Despite its age and a 14th century earthquake that knocked down the south side of the colosseum, most of the 150-some foot building is still standing. Like many ancient Roman structures, parts of it were constructed using a specific type of concrete. Scientists and engineers have long suspected a key to these buildings' durability is their use of this Roman concrete. But exactly how this sturdy concrete has contributed to the architecture's strength has been a mystery to researchers across the globe.A team of interdisciplinary researchers have recently discovered one answer to why these ancient Roman buildings have weathered the test of time — while many modern, concrete structures seem to crumble after a few decades. The answer: self-healing concrete. Curious about other new discoveries or potential climate solutions scientists are researching? Email us at ShortWave@NPR.org.