Upon first glance, Nördlingen has all the hallmarks of a classic German town. At its epicenter sits St.-Georgs-Kirche, a medieval church with an imposing tower that dominates the skyline, which itself is punctuated by the red pitched roofs of hundreds of timberframe homes and shops. But on closer inspection, it’s these very buildings that set Nördlingen apart from other towns, and for one very curious reason: These structures are embedded with millions of microscopic diamonds.

The diamonds are the result of an asteroid, which struck this area of Bavaria, a federal state in southern Germany, some 15 million years ago. The resulting impact left behind the Nördlingen Ries (or Ries crater), a massive depression that stretches more than nine miles across the German countryside, and is the site upon which Nördlingen sits today. The impact also created suevite—an impact breccia or course-grained rock comprised of angular fragments that can include glass, crystal and diamonds, and is commonly found at impact sites such as this one.

When the asteroid hit the Earth, the force caused graphite-bearing gneiss rocks in the region to form diamonds due to the immense pressure—believed to have been 60 GPa, according to one study.

“We assume that the asteroid was a stony one with a weight of [approximately] three billion tons,” says Gisela Pösges, a geologist and deputy director of the Ries Crater Museum in Nördlingen. “[We think that] the asteroid was a similar size to the town of Nördlingen, about one kilometer (less than three-quarters of a mile) across.”

It wasn't until 898 A.D. that the first settlers began to establishing what would become Nördlingen. During the Middle Ages, they began constructing the town's protective wall, which still stands today. (Nördlingen is one of only several German towns whose walls survived a long history of wars, including the Thirty Years War.) And to build each structure, workers gathered the nearest materials they could find—in this case, chunks of suevite.

“Our church, St. Georgs, is made of suevite [and contains] about 5,000 carats of diamonds,” she says. “But they’re so tiny—the [largest] ones are 0.3 mm—that they have no economic value, only scientific value. You can observe the diamonds only with a microscope.”

During the town's construction, the townspeople didn’t realize that the rocks they were quarrying for construction were the result of an asteroid. In fact, for centuries, locals believed that the massive depression was actually a volcanic crater. It wasn’t until the 1960s that geologists Eugene Shoemaker confirmed that the crater was the result of an asteroid. And it would be another decade before scientists ultimately analyzed the rocks and discovered the diamonds, estimating that the Ries crater contains more than 72,000 tons of the gemstone.

Today, visitors come from all over the world to marvel at this town of diamonds sitting within a massive crater. Nördlingen’s Ries Crater Museum regularly holds guided tours of the town, with specimens on display from the Ries crater and other craters from around the world—and beyond.

“We also have a huge lunar sample from Apollo 16 in our permanent exhibition,” Pösges says. “The astronauts from Apollo 14 and 17 trained here in August 1970, including Alan Shepard, Edgar Mitchell, Gene Cernan and Joe Engle.”

And while Pösges is quick to point out that other German cities and towns have buildings made of suevite, including structures in Munich, Augsburg, Leipzig and Berlin, Nördlingen has an abundance seen nowhere else on earth. It truly is a diamond in the rough.