History has blessed us with our fair share of puzzling structures. From the construction of the pyramids of Egypt to the mysterious origins of Stonehenge, countless amazing buildings and formations have left people scratching their heads.

With respect to the Wonders of the World, these beehive-shaped structures in the Middle East might just be the most bizarrely amazing piece of history yet. While they won’t garner the notoriety and fame of the pyramids, their purpose and design is genius.

Sure, on the outside, they don’t look like much. But what’s on the inside is truly impressive

During summer in ancient Persia—more specifically, modern-day Iran—people were in a constant struggle with the dry heat. With temperatures constantly rising above 100 degrees Fahrenheit, food spoiled fast.

The Iran Traveling Center

Of course, with no electricity and limited technology, they didn’t exactly have the luxury of a refrigerator. Therefore, residents needed some creative thinking to survive the scorching summers.

The Iran Traveling Center

That led to the development of these bizarre structures, known as the yakhchāl. They’re the ancient equivalent of a modern day freezer. They were first constructed around around 4000 B.C. For reference, the Egyptian ruler Cleopatra lived closer to 2017 than to 4000 B.C. In other words, the technology behind these things was insanely ahead of their time. So, how did they work?

Pastaitaken / Wikimedia

In the winter months, when temperatures were cooler, the ancient Persians would funnel water into these structures using a network of aqueducts. This water usually came from the mountains and, along its journey, was shaded by a man-made stone wall, which kept it cool along the way.

Yakhchāl walls were constructed using a water-resistant substance known as sarooj, which is made with a combination of egg whites, ash, goat hair, sand, clay, and lime. Sarooj is resistant to heat transfer, so once the water settled in the yakhchāl, it started cooling—and freezing—right away. Isn’t it incredible that they had this ancient technology all the way back then? But that wasn’t all…

Ggia / Wikimedia

At the base of this cone structure, small holes allowed the cooler, low-to-the ground air to trickle into the underground chamber that held the water. Meanwhile, the walls of the yakhchāl, which were at least two meters thick, channeled out the rising hot air.

Ggia / Wikimedia

As the incoming water eventually froze, the ice was either moved into separate chambers, removed to be sold and used, or added to the pool of cooling water to help speed up the freezing process.

The ice produced by a yakhchāl was not something exclusively reserved for the upper class, either. Shop owners utilized the ice to preserve fruit, while donkeys carried chunks of ice that were then sold to any interested buyers. Usually, they were built close to cities, as well.

The ice from a yakhchāl served a purpose beyond food preservation, too. It was used year-round to create faloodeh, a dessert made with thin noodles and a sweet syrup similar to a sorbet.

The Persian Fusion

It’s incredible what the ancient Persians were able to do with the limited resources around them. And traces of this ingenuity still exist beyond the remains of the structures; in some Middle Eastern countries, yakhchāl is a word for refrigerator!

Yakhchāls may look simple on the outside, but on the inside, they pack a serious functional punch. It’s crazy to think that ancient people had this great of an understanding of heating and cooling.

Give yakhchāls some love and share this crazy structure with your friends!